So, not knowing much about how hashtags work, is it possible that it was added from an external source?
Unless someone hacked into the account, hashtags are used as a way to draw in people interested in a subject to different media posts. They're key words that are searchable to get content viewed. So in this case, anyone who wanted to look for content with that hashtag of mgtow, they'd put that in a search and it'd pull everything with that specific hashtag.
And they are put there by people who upload the content, or someone who has access to the account. External sources do not hashtag that I'm aware of.