This is northern speaking. In the south they usually say ly và cá. Means exact same thing. Like soccer in america but futball elsewhere
Ly is different. Ly is a glass or glass-like, usually tall and smaller at the bottom. Ca is usually wide and the bottom is not much smaller than the top.
I usually see it as a general word for all cups, but that could be just my family
I don't get it is the fish in the mug?! even my ears can see that sentence!