The phenomenon described in this thread — visible haze or mist emerging from cabin air vents on a commercial aircraft while at the gate, without an accompanying burning or electrical odor — is almost certainly condensation fog rather than smoke, and it is one of the more commonly misunderstood non-events in commercial aviation. When warm, humid ambient air is introduced into a cabin that has been cooled by the aircraft's air conditioning packs (or when the packs are pushing cold, dry air into a warmer, more humid cabin environment), the temperature differential causes water vapor to condense instantly into visible droplets, producing a fog-like mist at the outlets. This is physically identical to what happens when a cold soda can "sweats" or when fog forms over a lake on a cool morning — it is a straightforward thermodynamic process, not combustion byproduct. Pilots and ground crews in humid climates (Florida, the Gulf Coast, Southeast Asia, the Middle East) see this regularly, particularly on hot, muggy days when an aircraft that has been sitting in conditioned hangar air or running APU-driven air conditioning suddenly interfaces with saturated outside air, or vice versa.
For working pilots, understanding and correctly communicating this distinction matters operationally and from a crew resource management standpoint. A flight attendant or passenger reporting "smoke in the cabin" triggers a completely different response protocol than a benign condensation event — smoke or fume reports typically mandate immediate checklist execution, potential engine/APU bleed air isolation, diversion or return-to-gate procedures, and in-flight scenarios can escalate to emergency descent and evacuation planning. Because "smoke" is a trigger word embedded in FAA/EASA emergency response training, crews are trained to treat any report seriously until proven otherwise, which means false positives carry real costs: delays, unnecessary maintenance write-ups, and psychological strain on cabin crew and passengers. The critical differentiator pilots and flight attendants are trained to assess is smell — true smoke from an electrical fault, bleed air contamination (oil or hydraulic fluid ingestion into the pneumatic system), or overheating equipment carries an acrid, oily, or electrical odor, whereas condensation fog is odorless. This is exactly the distinction the original poster intuitively made, and it's a useful diagnostic heuristic reinforced in initial and recurrent crew training.
This topic also intersects with a more serious and higher-stakes issue in the industry: bleed air contamination events, sometimes called "fume events," which have drawn increasing regulatory and media scrutiny over the past decade, particularly on aircraft using engine bleed air for cabin pressurization (as opposed to the Boeing 787's electrically-driven compressor architecture, which sidesteps this contamination pathway entirely). Genuine fume events involve pyrolyzed engine oil or hydraulic fluid entering the bleed air system, producing a distinctive "dirty socks" or oily smell, and in rare cases have been linked to crew and passenger health complaints (aerotoxic syndrome claims), grounding decisions, and lawsuits. The visual similarity between benign condensation fog and the early visual cues of an actual smoke or fume event is precisely why airlines train ground and cabin crews to rely on olfactory cues, not just visual ones, and why maintenance logs distinguish between "haze reported, no odor, resolved" versus "smoke/fume event, checklist executed."
Broadly, this Reddit exchange reflects a recurring theme in aviation: the gap between passenger perception and operational reality. Viral videos of "smoke" pouring from vents circulate regularly on social media, often provoking panic, and airlines occasionally have to issue public statements clarifying that condensation, not fire, was the cause. For pilots and aviation professionals, this underscores the value of proactive passenger communication — a quick, calm PA explaining condensation fog can prevent a viral misunderstanding from becoming a diversion request or a spike in ACARS/maintenance calls. It also reflects why crew training continues to emphasize multi-sensory assessment (sight, smell, and even sound of the air system) over any single cue when triaging in-flight anomalies, since visually dramatic but harmless events like this remain one of the more frequent sources of non-emergency emergency calls in day-to-day line operations.