Isn't this just a list if those with the highest average UCAS points of people taking up places
That's exactly what it is, yes. Plus a bunch of other measures to achieve a rank according to "our independent and trusted methodology, comprising entry standards, student satisfaction, research assessment (quality and intensity), graduate prospects, student–staff ratio, academic services spend, facilities spend, good honours, and degree completion."
...presumably lots more will have done the same, but will only take up one place - hence all of them will appear oversubscribed.
It doesn't make any mention of oversubscription; entry standards are all about UCAS points.
Two of the criteria used are the "average UCAS tariff score of new students entering the University" and "how satisfied students are with the quality of teaching they receive". It is the disparity between these two measures which the Independent article is picking up. They seem to be surprised that the universities which accept students with the most UCAS points don't necessarily have the highest quality of teaching (as measured by the opinion of their students). Frankly I've have been surprised if there was
a direct correlation between the two.
The one item I picked up from the table was that out of a possible score of 1000, Cambridge scored... 1000. However, although it ranked top in terms of UCAS scores of students, it didn't rank top in terms of student satisfaction with teaching quality - that honour went to Coventry. Bizarre.