Shakespeare Quotes: Hot blooded
If we look at the meaning of what Falstaff says, "hot-blooded" is more about passion and lust than anything else. Nowadays, this phrase is used to talk about anger, too. If someone is hot-blooded, he's got quite a temper. Yet, we don't think that's too far off what Falstaff means here. Anger, lust, and passion are all really strong emotions that are usually related in some way. So if you think about it, the context has changed a bit, but the meaning hasn't changed too much.
Plus, when Shakespeare uses this quote in King Lear only a few years later, he's definitely talking about anger (not lust).