In English, the infinitive is conventionally given as the base form of the verb, e.g., "to play;" whereas, in Gaeilge, the form that's conventionally given as the base form of the verb is the imperative, i.e., "play!" Irish language dictionaries and grammar books (and apps) give "imir" as the base form of the verb; in Gaeilge, "imir" (or "imir!") is how you would tell ("command") someone, "play" (or "play!").
I am not sure there really is an infinitive form in Irish, unless the infinitive is really the same as a verbal noun, but I'll leave that subject to the grammarians.
More to the point (the present point of learning the language), does it really matter whether we get the infinitive (if it even exists) of the verbs or not? Instead, we get the imperative. Does that difference really affect how hard or easy it is to learn?
If the kids pick it up fine as is, maybe we should do the same: accept it as is, without distracting ourselves with grammatical nomenclature.
Nothing against grammar, of course; grammar can really help us to learn and comprehend, and some people learn better through studying grammar. I'm just suggesting, maybe just accept the form the app gives us, and pick up and go with that.