The starring rodent -pets are usually cute hamsters so there must be something inherently evil about gerbils. Super Dude is the smallest character on the Simpsons so he could easily scurry away unnoticed. Gerbils don't vocalize much. That might explain why Burns' assailant is not heard during the struggle with Burns. Gerbils have large front teeth which explains why Burns thought Super Dude was smiling.
Gerbils are nocturnal.
Super Dude was sleeping all throughout his 'burial'. The Super Dude theory sounds like something Matt Groening would probably do just to try to throw everybody off. Super Dude is the pet of the grade four class.