He's portrayed effeminate in the later portrayals, whereas in the early Greek art he was portrayed as a bearded man, therefore both representations are correct
Not to mention, being a god definitely gives you the ability to disguise yourself, and that this is a fictional story where the creator has taken multiple creative liberties, so it wouldn't be surprising if they give Dionysus beard too
But hey it's a theory, Dio is a fun guy let us have fun :D
Damn, the author is really doin a good job of keeping me guessing on this foreign god. Zeus/Jesus/Thor/Neptune/Apollo?