Pichu HS + Ditto TW

[RB Golbat]

My Pichu uses Playground. I decide to fill up my bench, and put Ditto TW on the bench as well. Since my opponent chooses their Pokemon after me, They would only be able to choose Pokemon up to 4 bench slots, not 5 bench slots and discard the last Pokemon, correct?

 

[PokePop]

Well, if they're not playing a 5th Benched Pokemon, what would they be discarding?
They're not placing a 5th. Nothing to discard.

Now, if the opponent already had a full bench, then they'd have to discard one.