Was the area above the fan able to be viewed? If so, does the vertical portion of the vertical/wall firewall extend up to the roof? I mention this to rule out whether the d/wall on the ceiling was added after original construction.
All things equal… there may be 2 issues here. But simply put, if you can’t see the firewall extend and properly divide the living space and the garage you should call it out, whether it’s that the fan violates the integrity of the firewall OR that you can’t see/confirm the firewall, this is up to you as you were there. Basic firewall construction and protection is just that … basic.
The fan/pressurization issue is another one entirely… fuel burning appliances and so on.
Speaking of Dry-Walled garage ceilings
I see a fair amount of Dry-walled garages that originally were just a firewall that extended up into the trusses or roof framing and unfinished studs and walls, kinda like an unseedy club. Well, many times the drywall is put on after the fact by a less than knowledgeable contractor or a Home Owner and creates an area with NO ventilation, just Damp Framing Then a few years later, Saggy Framing. If you haven’t seen the movie Soggy Framing Boys by the COHN Brothers… it’s a goodie BTW.