Definitely. Meta is studiously only sharing the number of accounts registered. We have no idea how many of those are active. If we go with the old 1-9-90 rule, only about 10 million of those 100 million will become active users. Although, the rule obviously isn’t a universal constant. On the fediverse, for example, it’s closer to ⅓ of registered users that are active.
There are literally, not exaggerating, over one billion Instagram accounts in existence. It’s self-evidently not the case that they have just silently registered everybody a Threads account and are counting those numbers.