Does the opponent get to draw up to a full hand after being attacked with Pilebunker?
The turn order is:


Do one of these: move, push, attack, or dashing strike.
If you did an attack or dashing strike, your opponent must respond or he loses the round.
Discard any cards played this turn.
Draw until you have 5 cards, then your turn ends.


Your opponent playing Pilebunker is part of step 2. You still get step 4 this turn (if you successfully blocked), so you still get to draw back up to a full hand of 5 cards.

Source: Rulebook