tl;dr GPU drivers made by various vendors do not sanitize compute unit hardware scratch memory between uses, so you can just freely read whatever the last user left laying around when they stopped.

Literally too incompetent to follow even basic security 101 practices. A time shared device must be sanitized between users to prevent state leakage. There is no reason to believe that a security culture that clueless when developing a universally shared, high criticality device can be believed if they claim to do better elsewhere. Their process is either so incompetent or so inconsistent that their claims can not be believed without external audits.

In this case: Apple, Qualcomm, AMD, Imagination.

Edit: Added Imagination as noted by reply.