I think the sunnah is the man decides the amount he is going to offer anyway.This guy's pride demanded $20,000 for meg during the nikaah event, and he became speechless. The sheikh asked him several times if he agreed to it. He accepted the 4th time when the sheikh asked him. But the way he accepted ot sounded like a defeated man.
Fyi, there is a way to go around a woman dropping a high mehr on you during the nikaah event. If she wasn't willing to acknowledge what she wanted for mehr ahead of time, that is a red flag. The man and the woman should come to an agreement before the nikaah event takes place.
And if she changes it and surprises you during the mehr, you should let the sheikh know what you and the lady already agreed. The sheikh would do the mehr based on what you already agreed. Let her be the one that opts out if she doesn't get the high mehr.
Why would he allow that to happen, this man has no backbone