You mention private addressing allows you to change your hex code every month - did ElonJet lose tracking on a monthly basis? I don't recall anyone ever mentioning it, but I never followed the account.
If Elon was offering the guy money to stop tracking him, I assume he was at least taking the basic steps of changing his hex code and not doxing himself with the tail number. If he was doing those things, it suggests someone is in a position to identify the plane quickly and reliably when a new hex code is issued (which requires stalking, unless they have direct access to a database). ElonJet as a concept always struck me as a weird "why do you care" project, but it seems a bit more off and obsessive if he had to deanonymise the plane regularly to keep it going.