My experience (at least in the US and UK) is the opposite. A pumpkin is a very particular (usually round and orange) type of squash. Squash is the generic term for most of the vegetables (both winter and summer variety) that are eaten.
I've really only seen "Pumpkin" used more commonly in Australia, where I was surprised to see someone refer to what I knew as a butternut squash as a pumpkin.