A few things:
1. The whiffs were kind of low, but I'm not entirely blaming him. I'll explain why in a moment.
2. Here are two of his strikeouts that were of the non-swinging-variety.
The Cartaya PA obviously had two pretty wasteful pitches, and both had a pitch a bit too center cut (both were fouled). But the K pitches for both were watched and they were nasty and perfectly placed. So on one hand, each guy probably should have done more on those fastballs, on the back end, each strikeout was well earned. That's kind of the Cade Horton experience - he'll bully your ass with fastballs early and then get you looking later.
I'd like to see more whiffs in general, but just on this start itself, I think it's probably a red herring more than anything.
What impressed me most was that I thought he was done after 4. He left a slider center cut for a HR and a fastball over the heart for a long fly out to RF and thought "oh, he's gassed". Then he came back out and bullied the last three hitters. It was nice to see.