Hmmm, that could get confusing. Mastodon does not appear to understand lemmys sublemmy format of !sublemmy@lemmy.domain but if you format it with the “@” it works. As an example !monero@lemmy.ml does nothing while @monero does. However, regular lemmy users use the “@” as well, so to mastodon a sublemmy and a standard user are exactly the same.