What were people expecting ETH to do? He was asked a direct question. He had several options
1) Tell the truth, without actually criticising because it's simply other people were better.
2) Tell the truth and call out Sancho as a lazy good for nothing
3) Lie and say he was injured / ill
4) Deflect and say something about it's not who is not here, there was enough talent to get the job done.
5) Call the reporters all fecking stupid & headbutt the nearest one on the way out.
He chose option 1, which was to the point and the truth as he sees it. Not bringing someone who hasn't trained well is surely what we would expect. Does he leave out people who have trained better, just to accommodate Sancho? If he does that they can then (rightly) accuse him of playing favourites. It's a no win job our manager role. When he left out Marcus Rashford onto the bench last year he was hailed for doing it. Option 4 might have been more wise, but experience and emotions can play a part. Too honest is a fair criticism.
As for Sancho himself. Obviously the statement in public wasn't wise, but if he was feeling somehow attacked then it's understandable. If you read it you see he hasn't mentioned ETH or the club, just people. He can just as easily be calling out people who have interpreted ETH's comments as he was lazy, late etc when in fact he knows the real reasons. Perhaps he wasn't interpreting the tactics ETH wanted well enough and they had a frank discussion about that. Simply we don't know, but speculation is all about his attitude etc because people have axes to grind, pre conceived ideas about him etc.
Everyone is so quick to jump to the negative these days when not in full possession of the facts. I hope to god one day this toxicity and dark mood lifts, I really do.