You are right.
A polyfuse "blows", just like any regular fuse, because there is running so much current through it that it heats up. In a regular fuse that means so much current causes a thin wire to simply melt; in a polyfuse it means that a small piece of conductive (polymer) plastic gets so hot that suddenly its resistance increases dramatically, so that it gets hotter still, and things escalate to a point that the resistance goes so high that most of the current stops flowing. After the current is turned off, a long time after the fuse has cooled down the fuse slowly regains it original state and in the end becomes conductive again.
Always learning. One more tool in my bag of tricks.