Chiesa not tapping there was a technicality. He couldn't get out of that position and was hoping to hang on until the bell. Plus, even though he successfully defended that choke once before, Lee got that one in DEEP and it looked like Chiesa went limp because he stopped hand fighting the choke. That was why Mario thought he went out. It wasn't a good stoppage by any stretch of the imagination, but it wasn't highway robbery either. It was just a fight that was ending in 10 seconds that got ended in 5 and Chiesa was awake enough to protest. Lee was clean under the chin, Chiesa had nothing by way of defense and wasn't resisting the choke. A guy with a RNC like Lee has finishes that 10/10 times. I actually feel bad for Lee because he was brutalizing Chiesa from that back mount and that would have felt like a much more emphatic win without the stoppage.
But here's the thing. We were just talking about the responsibility of protecting the fighters in the Tim Hague thread. Chiesa was locked into a choke, looked glazed over, and his hands weren't actively working on defense. He looked unconscious. Mario would want that one back, but Chiesa probably can't in good conscience say he had a chance of escaping that one. I haven't heard any post fight press, but I would imagine once he gets to the back and looks at the tape he'll probably come to terms with it. He allowed himself to get put in the worst kind of spot.