Serveta had just gotten on her plane back to Sweden after her very loud, very abrasive visit to Mordhaus for whatever reason. It wasn't your business to know, she was Skwissgar's mother, that was a good enough reason.
He didnt see her go, letting a you escort her onto one of Dethklok's very kushy private jets in hopes she would just get off his tail about the whole thing, remaining exactly where you saw him last- slumped by The Big Window ™ as he put all of his everything into playing his Gibson, his eyebrows creased uncharacteristically.
That woman just bothered him, and after that shit she pulled with his step father after all that searching for a father figure made him actually want to commit matricide in the most brutal way possible. It wasn't fair.