Mitchell admitted to being a germaphobe. There is nothing wrong with that and I don't think anyone is blaming him for his initial reaction but it's a irrational fear and one that shouldn't have affected how he handled things after the storm settled.
The most plausible thing I heard was that Rudy had visitors from Europe and Mitchell blamed Rudy for bringing in Covid, alongside his reckless behaviours. The thing is though, Mitchell was touring high schools in New York and shaking hands with students. Tough to say he was extra wary of Covid.