I haven't seen actual video of the first "final whistle", but written reports do read like he was immediately corrected on that one, presumably over comms.
And the second final whistle came with only 13 seconds of the match left - close enough that a dodgy watch or the ref starting his watch a little early could explain him thinking it was 90. The decision not to add any added time is technically his - so while it would be very odd not to play anything extra given the 2 penalties, red card, associated VAR checks and substitutions, I don't know if that is technically wrong to the extent that the other officials would be obliged to insist he played additional time?
Don't get me wrong, it's all very odd and despite this:
https://www.bbc.co.uk/sport/africa/59981733 I don't think it's over. But there's a limit to what the AR's and 4th can do if the referee is insisting the game has finished and won't be persuaded otherwise?