I'd dispute that.
He was on the verge of being sacked prior to that Lee Martin cup goal.
His tactics and playing style were never anything special or revolutionary, in fact not much different to Mourinho, Solskjaer and now ten Hag... defend in numbers, soak up lots of pressure then hit the opposition on the break by hoofing it up to speedy forwards.
It's just thanks to the timing of the inception of the PL and SKY money becoming a thing he benefited massively as united were the most commercially attractive club at the time with all their Asian fan base to tap. So he was able to massively out spend every other club in the league for a period of time.
Throw in the favourable treatment that united received from the officials and its no surprise he achieved the success and dominance that he did.