Really Quick Fast Casting Questions (like lightning)

Actually, it could also be interpreted as:

"Thus, a magus can not cast more than
A) one normal spell, or a fast cast
and
B) a normal spell
in the same round."

... which would mean that a magus could definitely case two spells in a round, but only one of them could be a fast-cast spell.

I'm confident that this third meaning is not the way that the writer intended the passage to be read, but it does show very clearly how careless wording can lead to ambiguity.