Can a clogged catalytic converter destroy a transmission?

I have a 93 mx-3 v6 auto, that was slipping, brought it to the famous national transmission place. I provided them a trans. They tested installed it and test drove it no problem, I picked it up and it didn't have overdrive, drove it back to them (less then 10 total miles). They claim they bad cat killed the last one and this one and turned the fluid black already. Is this possible?