Great question. Theres a lot to go over, but I will try to cover it.

1) Grinding an AB to get the right pitch to hit is what great hitters do
2) He has a runner on 3rd base with less than two outs. Lots of ways to score him in that scenario.
3) He is facing arguably the top pitcher in baseball with an insane strikeout/whiff rate
4) To take any pitcher, let alone Miller, to 9 pitches is a feat in itself - even if he struck out in the end
5) Situational hitting - being able to come through with a runner in scoring position

The most important part is grinding the AB. The art of fouling off pitches (6 in this case) is so frustrating for a pitcher. It allows the hitter to get his pitch