I once set out to learn Vi, but the absurd modal editing and convoluted key combinations for basic tasks made it a nightmare. Efficient and logical, my ass!
ctrl-f and ctrl-b are the one I use frequently and amongst the first ones I learned.
But I suspect he meant "sequence of keys" by "key combination" in what was clearly intended to be a humorous parody of the previous comment.
I have more respect for vi's key bindings though because they are, in fact, quite efficient. But I only know enough vi for basic editing.