4 DFs as a whole doesn’t look that bad.
But if we analyse it in detail.
4/17 = 23.5% of his second serves were DFs.
That’s still pretty terrible and it’s not a good look. If he has a great serving percentage like today, it won’t be that detrimental, but 84% first serve is a rarity, not the norm. It was like that in WTF, but in ATP Cup the percentage wasn’t high and the DFs rained. On an average serving day, he’ll still serve way more DFs since he’ll have more second serves in play, so still not really an improvement in that regard.
If his DFs per second serve percentage is lowered a lot more, only then we can say he has improved in that department. In this match, despite the win, he still hasn’t.