There was a BBC article a couple of days ago, saying it had been reported he was helped by a band.
They came to his place then left with him hidden in an instrument case (I would assume a Bass).
The airport part is not clear, but either they not very thorough when checking instruments for private jets, or they bribed someone I guess.
Doesn’t Japan have exit controls?
Did they sneak him into the airport as maintenance personnel and then get him on a plane?