I do know that it has been my experience and that of other users that interactions here are at a far higher rate (ratio'd to followers) than on Xitter -- FAR more Likes, RTs, and replies for the lower follower/following counts we tend to have on Mastodon (vs Xitter).
This tells me that a much higher percentage of accounts here are active and frequently used than there.
You also cannot base your data only on the Mastodon app user count. There are multiple apps to access #Mastodon and the #Fediverse, including #Tusky#Moshidon#Megalodon and #Tooot. Not everyone accesses Mastodon through the same doors.
FYI... At last count, #Bluesky has around 5 Million users and #Mastodon has around 15.5 Million users. Unlike #Xitter, none of the Mastodon accounts are bots created merely to build the follower counts of celebrities, manipulate voters, and bring in ad dollars.
Almost all of the accounts here are real people engaging in positive, uplifting feed. Trolls have no algorithm to help them build a following. Ads are not allowed.