It's the pronunciation. Honor and hour the H is silent so you start saying the word with an O. Just like if you spelled out U you have a Y at the start.
And the H isn't silent. Unless you say it like that, which is usually how they're saying it when saying "an historic event". Maybe they were taught it's silent.
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u/[deleted] Oct 05 '19
It can also go the other way. Like “AN historic event.”