I wonder what do you understand by the definition of advertising. It's okay to
invite your friend(s) by pm, discord, etc. Inviting in public chat is actually an alternate to draw players' attention to another server. Therefore, inviting a player or players publicly isn't allowed. If you see players inviting other(s) in another server, the first step is to urge/inform them it's not allowed. Then, you may report.
nvm, considering it as a misunderstanding, I'd follow what I said. Consider it as a verbal warn and don't invite any player via public chat again. You have got other means - that don't pull other players' attention to your msg.
Solved.
Thanks for reporting!
ps: Just to clear out the things, inviting your friend by PM and inviting random player(s) by PM has the difference.