Errors are a huge hole in how baseball accounts for what happened. A single is a single, it puts a guy on first. A strikeout is a strikeout, which is an out 99.9% of the time, and if it's not someone notes that there was a passed ball/WP.
But an error... it could be four runs. It could be nothing at all, on a dropped foul pop up. It could be because of a bad hop. But there's no error when a player has a terrible lapse in judgment, so failure to call for a routine fly ball is recorded exactly the same as a lined shot up the gap. There's no differentiation (in the official records) of a throwing error vice a fielding error. I'm guessing the error rate in the late innings of no-hitters is significantly higher than otherwise. Errors and un/earned runs are pretty close to breaking the accounting of box scores, which should tell us what happened so we can reserve judgment for later.
This article is very informative about his evolution. Without the velocity, he has to maintain the sharp quality of all 4 pitches plus command to maintain his current production. It's likely hard to keep that level of sharpness. But he also sounds like a guy that has learned a lot the past few years and adjusted to the stuff he now has vs. the stuff he used to have.