I don't think allowing US residents withdrawing BTC or fiat makes them a money transmitter.
i'm not sure about bitcoin, but in the case of fiat it certainly does.
from the case of btc-e and alexander vinnik:The indictment charges BTC-e and Vinnik with one count of operation of an unlicensed money service business, in violation of 18 U.S.C. § 1960, and one count of conspiracy to commit money laundering, in violation of 18 U.S.C. § 1956(h).
bitfinex wired funds to USA customers for years. 18 U.S.C. § 1960 says:
the term money transmitting includes transferring funds on behalf of the public by any and all means including but not limited to transfers within this country or to locations abroad by wire, check, draft, facsimile, or courier;
The banning of US persons was most likely related to margin trading, margin lending, and a subset of listed coins potentially being classified as "securities" by the SEC.
The CFTC looked into their business practices in 2014/2015, and fined them based on their margin trading practices. Presumably, if there were concerns about their "money transmission" practices, the CFTC or another regulator would have stepped in.
the CFTC has no jurisdiction over money transmission issues and i don't think anyone was particularly concerned about bitcoin exchanges in 2014. like i said, federal agencies spend multiple years building cases like this. and this isn't like btc-e where the investigation was all under seal; there are multiple active investigations into bitfinex right now.
i certainly don't wanna see them go down and i want to think they won't, but i wouldn't be storing money there either. that's risky as hell.