Yeah, I think that's right. But it does raise an interesting point. The meta-point of the study was a good one, I think, which is to "study privacy on the internet".
I'm soooo behind that (one reason I am disappointed in the ethical lapses here)—I've often considered publishing the steps I take for each website on a substack or whatever, to help other people. Sometimes, it can be hard to figure out (1) if your data can be requested-to-be-deleted, and (2) how to even do it.
Clearly, the deception was bad; I guess, just thinking out loud, how could this study have been done ethically? Perhaps, sign up real people to request the data, and transparently include a notice that this was part of a study?
The last bit is the tricky one; including that might skew the results in favor of websites being compliant.