That will depend on the definition of paid wouldn't it? It could just mean "we have 38M credit cards" we can bill.
I mean if they include people who didn't actually pay in the category of "paid" members, that would be a lie, no matter how you look at it.
There is no such ambiguity in the definition of "paid". Cue separately disclosed the trial users (8M) from the paid ones.[1] So there are actually 46M Apple Music users.