No it's not a joke and yes it's valid grammar. If you're going to correct someone's grammar, at least know what you're talking about.
https://www.quora.com/Which-one-is-correct-a-history-or-an-h...
https://www.quora.com/Which-one-is-correct-a-history-or-an-h...
The rule is "an" is used in front of a word that starts with a vowel sound[1]. "An hour" is correct because the "h" is silent. All modern (native) English dialects pronounce the "h" in history, ergo "an history" is incorrect grammar.
[1] https://en.wikipedia.org/wiki/English_articles#Distinction_b...
from the first sentence.
> Quora
> not a high quality reference
> proceeds to reference Wikipedia
Source: https://en.wikipedia.org/wiki/Elision
Well, the grammar rule got a name. It doesn't say whether it applies to "a[n]" history" though.