It’s not a normal tobacco plant.
They engineered genes designed to produce monoclonal antibodies and injected these into tobacco plants. They probably could have chosen any plant.
No, tobacco is fairly unique in this regard, to the point that it’s highly preferred for such purposes. There are several other instances of tobacco plants being used in this manner going back some time.
Duckweed is another candidate.
Pharming. (Not the Interwebs attack)