Its hard to say for certain. Patreon padding is usually within a community, and not so much an insular individual thing. Alex could be in theory padding his total revenue, but padding users is a lot more annoying, and unlikely that he's doing so either way, the numbers don't really support it. If he was padding, he'd pad right up near an upper middle class income, not compete at the bottom with wagies.
The simpler reality is that the way he appeals to children with this game, plus the growing number of kids with access to their parents credit card for various online subscription platforms. They're used to buying subscription services for all sorts of things, so patreon for a videogame they think they like (They're often really in love with an unrealistic ideal of what it could be, not what it is, as any of us who gamed as kids probably experienced) is completely normal for them to engage in.