Three simple facts here: 1) This is obviously abnormal enough for the people in the video to flee 2) the aftermath - (1:15+) - clearly demonstrates it was unsafe to be there and 3) there is no way to predict if the next eruption would be equally abnormal or worse unless one were trained in this field
There is no arguing those facts, it's 100% clear from that video you linked. Am I going to stay away from the park the rest of the day? I don't know, maybe. It really depends on the circumstances. I am not a volcanologist. I'm not even a scientist. I don't understand the specifics involved here. If it were me, and I can clearly see something abnormal happened, I would NOT risk going back unless I can somehow verify it was safe to do so. That's common sense. It might involve finding a park ranger to speak with or calling the ranger station to get more information. I've been to the geyser at Iceland where they have signs that explicitly tell you about the unpredictable nature of it and how people have been badly burned. This is not a no-risk situation, especially when the situation is not the norm.
I've been to the big island of Hawaii during volcanic activity and they explicitly tell you to stay away from it due to the gasses, rocks, lava, etc. Maybe that elevates my skepticism over the safety here, but it seems that's for good reason.
EDIT: here you go mate, you don't need to look at Hacker News comments. Take it from the Park itself:
https://www.nps.gov/yell/learn/news/240723.htm
> Biscuit Basin, including the parking lot and boardwalks, are temporarily closed for safety reasons. The Grand Loop Road remains open.
> Park staff and staff from USGS will monitor conditions and reopen the area once deemed safe.