Not entirely sure whether or not this is spoilers at this point, but I'll put it as one just in case.
It does not explode if you beat it normally. You have to defeat Bass buster only during the second phase.
You can pick up the adapter, but don't use it. Once that's done, you'll get slightly different dialogue from Bass.
Upon attempting to leave, you'll be forced into a fight with the Wily Capsule 7, the boss Bass replaced in v5b and later.
After defeating that boss, now the castle will explode into flames in the credits.