Does VACUUM FREEZE do something extra or special than to defer autovacuum for an extra 50,000,000 transactions?
It effectively resets the pseudo-counter(s) that autovacuum uses to determine when next it should perform an aggressive scan. Or, put differently, it does exactly what autovacuum would do when the pseudo-counter(s) hit their thresholds. The act of doing that thing effectively resets said counters to zero at that moment (absent concurrent activity).
That seems to be what I said. Or am I still missing something?