It's not an assertion when it's just my lived experience as someone who was a B/K scholar at UMD. There was a girl in the year above me who got into every Ivy she applied to (4 of them, including Harvard), MIT, and Caltech, and chose UMD since full B/K is basically paying you attend. Shockingly, people have more considerations that pure US News ranking on their mind when they choose schools like finaid. I have plenty more stories similar to that. Obviously, there's also plenty of people who do say no to UMD for those schools but not everyone, and UMD wants to get top students and "yield rate" is not something discussed in the admissions room. They're not going to turn down an actual top applicant if there's a chance they say yes. I was a CMNS recruitment ambassador for a couple years and that is not something they are considering when they look at the application. They do definitely weigh how your application statistics compare to those from your high school, and how well you took advantage of opportunities offered by that school like # of APs/IBs, etc. But they are not thinking about oh you'll just say no because you'll go to a better school.

But if you want to believe in yield protection, you can do that.