I can't say Man U played better than Newcastle, but I guess the home field factor played a major role... They were lucky in this match and to be honest their game was much better than the previous ones... Now Newcastle and Devils have the same number of points in the standings and there is a small chance to get into the Conference League if Chelsea lose to Bournemouth, which I doubt...
I was surprise Manchester United won the game last night against Newcastle United, there win against Newcastle United has given them a chance to qualify for the conference league if Chelsea losses to Bournemouth which I doubt just as you, but football can funny and unpredictable anything can happen Bournemouth can shock the world by winning Chelsea puting Manchester United in a better position to qualify for the conference league.
Bournemouth have sluttered Chelsea in the past before so if will not be a new thing if they win Chelsea and since the season is almost coming to an end some drama may occur so Manchester United may be the favourite to qualify for the Europa conference league though even as Manchester united won Newcastle yesterday, they have to put more effort in their next match if they want to end the season well.