Michael Oliver has a fine record of ignoring early nail on cautions. Match control (and his career) have always been more important than enforcing the laws of the game.
I see many refs at lower levels copying this trait where anything goes first 20/30
He took a gamble in letting things go early on, and it worked as he had complete control of the game even when it was getting heated towards the end (Gary Neville praised him for this).
There's a competency in match control for levels 4 to 2B which is below, and I would argue he correctly followed that and managed the game pretty much perfectly.
Recognition of the nature of the match from the start, correct attitude adopted from the beginning.