Yes, they can swell and do so as a safety feature, supposedly to let off gas without building up too much pressure so that it explodes. Apparently something went terribly wrong here. And a swollen battery should be replaced so the new generation of non-tactile touchpads can be a problem here. One of few ways of noticing a swollen battery before was that the touchpad didn’t work as well and felt “stiff”, and clicked easier than it should. Because of the reduced gap between the touchpad and the now swollen battery. However, with modern Macbooks, you don’t physically press it, but it’s instead a simulated haptic engine feedback.