Actually, the popularity of pneumonoultramicroscopicsilicovolcanoconiosis stems from it beng the longest word in the official Oxford English Dictionary, and thus, the longest word in the English language (disregarding placenames and the like). So it is a real word.

It is a lung condition caused by inhalation of silica dust.

From the Wikipedia page:
Pneumonoultramicroscopicsilicovolcanoconiosis is, according to the Oxford English Dictionary, "a factitious word alleged to mean 'a lung disease caused by the inhalation of very fine silica dust, causing inflammation in the lungs."

Also from the Wikipedia page.

"The 45-letter word was coined to serve as the longest English word and is the longest word ever to appear in an English language dictionary."

Besides, the fact that it is factitious is irrelevant. It does not make it any less of a word than it is.

Yes, it is a word, but my point was that it only exists for the point of being long. The actual definition for the illness caused by the inhalation of silica dust is silicosis. If I just made up a 46 letter word and gave it the definition of a word which already exists, that would just be pointless and stupid.

But your point was and I quote

"That's not acually a real word
The longest word in the English dictionary is antidisestablishmentarism"

And you just admitted that it IS a real word, nevermind the fact that it's pointless.
And I've just proven that it is in the Oxford English Dictionary.