The book's language is funny. I don't mean "like Jeff Dunham" funny; I mean "like Joker" funny. Cantrips are defined as 0-level spells, but, for the entire rest of the book (which, I might add, actually makes more sense if you read it back-to-front, skipping spell descriptions, then going back for those), you're supposed to read "spells" and "cantrips" separately. Your spells known/prepared and cantrips known are separate, wizards can transcribe spells, but not cantrips (Note: It is a pretty harmless house rule to take after the pattern that was set in previous editions and calculate them as 1/2-level spells for such calculations and allow them to be transcribed.), spells known by spontaneous casters and prepared by prepared casters can be traded out on level-ups and long rests, respectively, but cantrips can't, et cetera, et cetera . . .
To make a long story short, as odd as it seems, MPMB's notation of "both spells" is perfectly in line with the style that the book sets forth.
Also, by definition, cantrips are unlimited, so it wouldn't make sense for them to be listed in the Limited Features. If you enter in a Lv20 barbar or druid, you'll notice that Rage and Wild Shape take themselves off the Limited Features list, too, because they become unlimited.