Yes, but they said ambient temperature, and I assumed that to mean the temperature inside the garage (I grew up with a detached garage that was not insulated, it got very hot in the summer, especially when it's over 100F outside, so this doesn't seem outside the realm of possibility to me). It would be significantly harder to disperse heat from the CPU and GPU in that environment.

Open system with a box fan probably has better cooling than a mediocre, closed case. Cursory searching says 105-110F isn't too crazy for a closed case