Ngl, I'm so used to some rather very commonly used tropes by all the Mangas/LN/WN at this point, I just don't exactly care if it's "Trash Trope" or "Plot Miracle Trope". But that aside...
From what I understand, MC's real identity is probably kept as secret for sake of both MC (not have to deal with annoyance with fame), and the guild (get Very Good Skilled person, and no have to deal with annoyance of being middle man of problematic requests to MC), but only Actual Top of the Guild know about that... and despite what NTR guy thinks, he's basically still at bottom of the chain, just have enough power to did what he did.
And initially in the guild's higher up's POV, they thought MC asked to retired and NTR guy approved that, only to realize that NTR guy F**KED UP real bad by FORCING MC to retire. And for MC's Ex... considering NTR guy using that excuse, it would be inevitable that she would get dragged into the mess with the guild.