It's not silly. Hot glue is a little gun that heats up and melts glue sticks that one can use to stick things together like a tube on the glass or hot glue a divider in a large tank to hold 2 T's. It's a universal, nontoxic glue that can do a lot of things.
Are you talking about the sealant they use? Or are you talking about what the use to hold the glass together? Here are the answers to both: The sealant is a silicon caulk. The "binder" is either a a strong super glue, or (in the case of high-end tanks) melted glass. Of course, there might be other glues used for different brands, but this is what I know.
Well, yes and no. It is a good holding glue, it really wasn't meant to hold the amount of water that aquarium sealant is, but it really isn't anything like super glue.
Its great for building arboreal tanks, I use it for all of mine.