No one's life or health was in immediate danger so declaring an emergency just to set your pax free on the ramp wouldn't get any praise. In that situation and at that moment, inside the aircraft was probably the safest place for them to be. As a matter of fact, sending them out on the ramp to wander around in a thunderstorm would immediately endanger them instantly.

Someone mentioned an APU fire. That is a REAL emergency and then you would be right to evacuate. What if this was a larger aircraft? Would all the folks that vote for an evacuation blow the slides for the 400 passengers and crew on a 747? How about a 737? If you answer no, then you shouldn't evacuate an ERJ either in this situation. This was uncomfortable for sure but was by no means an emergency situation.

As for passenger accounts. If the lav stinks it is "overflowing". If it truly was then the entire aircraft would have to be disinfected before allowing the passengers back on. A really overflowing toilet is a biohazard.