I think the big upset with Goff is not that he's leaving nor who said what when. Trades happen regularly; it's just part of the business of football.
It was that just like with everyone who learned of the trade, the structure of the deal made it clear that while of course acquiring Stafford was paramount, this was also the Rams paying a BIG price just to rid themselves of Goff.
Indeed Goff got it that it wasn't just that the Rams wanted to upgrade the position, they flat out didn't want Goff on the team anymore and they were willing to pay most anything to have him go. And the way the deal was structured, clearly nobody other than Detroit was even interested in having him around and then it was almost literally a price Detroit had to pay to get the 2 Firsts from the Rams.
That is just an unspeakable fall from a very high perch. Probably almost any of us would have been devastated by it and I imagine it'll take some time for him to get over it.