That source is a reply by Musk confirming a statement by another person (https://twitter.com/Timcast/status/1603748611896283137?s=20&...) commenting about Musk being enrolled in the PIA program. That statement also has a link back to the creator of the tracker themselves also admitting Musk's plane(s) are/were in PIA but they figured out how to track it/them anyway.