|He could be ready for potty training or not, I think you`ll have to look at other cues to really know.
My son constantly undressed and took off his cover & diaper at naptime (and played with the poop inside so count yourself lucky!) from the age of about 18 months onward but was absolutly not ready for potty training. My girls were even worse, taking their clothing, covers and diapers off all day long (and flung them everywhere and anywhere just for fun) for months before they were ready for potty training.
So yes, it could be a sign that he`s ready or it could just be that removing clothing or diapers is just a fun game for him.