From what I've seen, I wouldn't trust the MLS site (or ESPN, who are presumably getting their data from MLS) on reasons for sanctions. Half the time they are incorrect as I'm sure it is just some guy watching on TV back at MLS HQ who is inputting the data.
Very surprised they said the Seattle goal should have stood. But, by doing so, they justify the non-awarding of “weak” penalties via VAR. So there’s a means to an end here that allow them to be somewhat consistent. I can’t quite come to terms with the logic that play should have been stopped between the incident and the goal due to an injury, though. We are taking a matter of a few seconds. A referee is supposed to say “no” to the foul but “yes” to a (serious) injury stoppage in that timeframe? I don’t buy it. I think saying that a foul call would have been defensible but the absence of a foul call is not clearly wrong would have been a safer way to go.
I saw it as saying that injuries to GK are “serious” sooner than injuries to field players because of the impact of a downed GK. (But I agree that seems pretty quick to get to serious.)