If you are processing financial transactions (including something of “value that substitutes for currency”) between other people at their direction, you are a money transmitter. The whole point of both Bitcoin is decentralizing this function from banks to a network of miners, and a similar thing is done in Lightning with its nodes.
That's correct. In the case of Bitcoin, the thing that most closely resembles a "money transmitter" are miners but FinCEN ruled that they are not[0]. A sensible decision because otherwise, Bitcoin would have effectively been banned from the United States (or Bitcoin miners, at least).
