Well that's nonsense. Words have meanings for a reason. The meaning of the word "unlimited" is not, in fact, "limited, but we won't tell you what the limit is

Well that's nonsense. Words have meanings for a reason. The meaning of the word "unlimited" is not, in fact, "limited, but we won't tell you what the limit is — you'll get to find it out the hard way". Whatever the terms of the "fair usage" policy are, that's what should be in the description. Otherwise, is plain old lying and misreading — which for some reason you are OK with.