No idea, but that is not a completely safe way to delete data. It would only be safe where there is a unique field name that is never repeated in any ACF field group.
Not sure where you got that, but I don’t even remember writing it. I can’t even be sure I tested it when I wrote it. There could have been some change in ACF since then. A quick look at the ACF code shows the hook should still be firing but I did not do a thorough search of the code.
I can tell you that I’ve written a lot of code here that I’ve never tested and this would likely fall into the category of things I’ve never used or tested because I don’t use unique field names and I don’t have not worried about stray data in the database for a long time.
