Manchester United losing to an average team in League Two is historical. League Two even though has number two in its name, it's not the 2nd tier league in England. For anyone not knowing it, EFL is the 2nd tier league, EFL League One is third tier and EFL League Two is fourth tier. So, Manchester United lost against a fourth tier league team.
Since the formation of Premier League (and this tier system) Manchester United never had played a 2nd tier league but with their current performance, Manchester United might create a personal history by relegating to EFL. They'd perform better on that level and it would also clear the doubt about which is the real team in Manchester.