The reviewer apparently installed the fan in his/her attached garage to reduce the noise heard while the fan was running. The airflow was accomplished with a screen door between the house and the garage space. Sounded brilliant!
Except that it probably defeats the integral firewall built between the house and garage that the person door is part of and puts them at higher risk of fire spreading from garage to house and related risk of casualty.
Are you one of those people who actually parks their cars inside their garages?
I've never understood the logic of fireproofing the garage from the house when the entire kitchen is still inside the house. I understand that it's building code, but I wonder whether the extra expense is justified by the statistics.
I'm not trained in fire code so I can't give an official explanation, but most garages are filled with flammable and combustible stuff. Fuel, oil, paint, solvents, you name it. Add a vehicle that may or may not catch fire, and sometimes ignition sources like furnaces and water heaters like some homes have in their garage, and it's a pretty big risk. Part of the risk is that it's "out of sight, out of mind" where your kitchen is in your home.
In my case my garage is separate from my home so it's not a direct issue for me, but I understand some of the concern. 5/8" type X (fiber-reinforced) gypsum board when applied, taped and detailed correctly, creates a "1 hour burn rating" for the wall assembly, meaning it takes about an hour for fire to burn through it. Without it the wall may take only minutes to burn through. Any time you can add to the available escape time for home occupants is well worth it.
If you know your local firefighters they would be able to explain better than anyone I bet. As a designer and builder I have to follow code, but also think about these things when designing for residential clients.