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That's not a warning, it's a random insinuation. Take a look at

Please don't post insinuations about astroturfing, shilling, brigading, foreign agents and the like.

If I can prove an employee of the company is posting it but acting like a genuine person, can I do that?

It's mentioned in the linked thing - if you think someone's abusing the site, email the mods.

I mean, I am not an employee of JetBrains, so... I don't know where you're going with this