That guage is a thermometer not a thermostat. That style is also wildly inaccurate so with a reading of 100*F it could have been anywhere from 95*F to over 105*F.
Also I wouldn't be surprised if it really was 105*F right under all those lights.
I don't go into big box pet stores any more; I'd probably be trespassed from the property after I ripped the managers and staff a new one.