Its not because its an "AMD machine" its because he has higher end parts.
he has an rtx 2070 super and a 3700X, both of which could consume quite a bit of power,
but actually intel consumes much much more power than AMD, hitting 240 watts on a stock i9 10900k, while ive never seen a 3950x (a 16 core, unlike the 10 core i9, with similar enough single core) spike above 180 watts on stock.
a ryzen 3 and a gtx 1650 would obviously not need a 750 watt powersupply
as for bronze/gold, it doesn't mean much, its the minimum efficiency of the psu, but more importantly than efficiency is quality.
same with an i3 and a gtx 1650
while with an i7, and r7 with a rtx 2080 i would go with a higher wattage part.
non of these builds "need" a 750 watt.
even the i9 and an rtx 2080ti might(TM) run on a 550watt
but having around 100, or abit more watts is a good idea.
i would never, for any normal system go above 850watts.