Melted Distributor Rotor?

Engine died last night and got a tow home. Pulled the Distributer cap and Roto this morning. The rotor was melted and all its metal parts laying in the the bottom. The rotor arm has a hole melted through it and also looks like it is burnt. It also looks like there is a hole burned/melted thought it to the top of the distributor shaft?
I just replaced these a 150 miles ago and it was running great.
Any ideas as to whats going on?

sounds like there was something wrong with the cap and rotor, when u installed them, sounds like it was arcing.

I replaced rotor and runs fine.
The other cap and rotor were new 200 miles ago.
Must have been defective.