black tank mistake, not adding water after draining?

Never had this issue before, went to pick up my TT and smelled something odd inside. When I got home I opened the toilet lid and oh boy...there it was. The toilet smelled horrible, black tank was the obvious culprit.

I store my travel trailer on an asphalt parking lot in direct sunlight. It has been pretty hot here lately and im wondering if I left the black tank too dry after draining/dumping it at the last campground. I usually run the toilet for a minute and add a treatment at the end of a camp trip.

Is it possible that the little bit of water evaporated and left just the waste to bake in the tank?

if so what are my options on controlling the smell? Ive added more water and another treatment.