I agree.
There are plenty of colleges with low RD yields that don’t appear to do this. They just admit a lot of people, and then apparently yields are predictable enough that they only need to make modest use of their waitlist. To the extent they get unusually high-numbers applicants, rather than waitlist or reject them, they admit them, and then maybe offer them merit, honors, or so on. Obviously it doesn’t always work, but apparently that contributes to making their yields predictable enough.
So I agree it is likely it is not just a lot of low, but a lot of low and difficult to predict, RD yield cases that would lead to a lot of this happening at a given college. And it may be a contributing factor if they have little or no merit.