I thought if a pipe is too restrictive it could cause it to overheat or burn the piston up on the exhaust side?

Over restricting the pipe adds heat to the piston skirt on the exhaust port side of the piston as well as overheating the top of the piston. 

Where the piston fails depends a lot on how the restriction affects the rest of the engine.  If the restriction affects the volumetric efficiency it can have an effect on the jetting possibly burning the piston on the exhaust side.  If the over-restriction increases the piston crown temperature enough, it can lead to pre-ignition, then detonation and burn a hole in the center of the piston. 

An over restricted pipe can also change the engines fuel octane requirements.  Higher internal engine temperatures usually require higher octane fuel. 

An over-restricted pipe will not usually increase the coolant temperature significantly.