Yes, that was fast, but this is partly because of the introduction of channel giveaways a few months ago: channel owners can gift premium subscriptions to their subscribers, which will be randomly selected by Telegram (you don’t need to opt-in). The channel will then be awarded the giveaway winners’ boosts, that will let it unlock some additional features

That means that after some months, the giveaways winners will have to decide whether to renew their premium subscription or not (which was gifted to them: they might not be as interested in Telegram’s premium features as paid users that decided to subscribe on their own). The current number of subscribers might be a spike caused by the novelty of giveaways. It’s unlikely that the trend of gifting premium subscriptions will continue to generate this much revenue, but we will see. For sure this is a very convenient moment to decide to release some numbers on premium subscriptions ;)