What people think is a monopoly and the legal definition of a monopoly is different. You have to be able to show harm to e consumer, something's hat is going to be challenging to show with a handful of hidden APIs. APIs, it should be noted, that somebody could implement themselves (at least for the sample given; whether it would be approved is, of course, questionable).

On the other hand, it could be used as evidence of part of a larger anti-trust case, but given that Android devices are cheaper, perform just as well, and have a strong ecosystem, that's going to be hard to pull off.