Earlier quoted context omitted.
"An historical" actually is 'wrong' (for as wrong as anything can be in English, which generally isn't very). "Historical" doesn't make a vowel sound when read (which is the rule).
It does if your dialect has a silent H there. A lot of people that pronounce "an historical" do so with a silent H.
Maybe not silent, but definitely muted. It's a soft "H" and probably borrows its pronunciation from Spanish.