As some others said, Mycelium probably didn't do a proper due diligence. I saw 1xbit being promoted on some other legit sites too, so I guess that all these warnings on bitcointalk don't have that big of a reach, unfortunately.

Since they are not active on any socially media, I don't see any other way to contact mycelium other than via email, so if enough of us contact them, they might stop promoting 1xbit. Anyway, here is the email address support@mycelium.com