I don't think very much should be read into that Man U victory over Liverpool. Yes, 4-0 sounds quite comprehensive, but it has to be taken in context. It's not a competitive match, and not only is it pre-season, it's early pre-season and players are still getting fit. But the biggest reason is the players they put out, Liverpool made so many substitutions, they had over 30 different players appearing in total.

https://www.bbc.co.uk/sport/football/62141591