Maybe he came late and was davening shmoneh esrei before ברכת ק״ש.
This reminds me of whichever Odom Godol who said that everything Hashem gave us is for a purpose - and krumme logic was invented for being dan lekaf zechus. I was trying to think of one when I read the above but I read your explanation first.
Agav, since this is for random posts, the Kotzker asked why the mishna says מִי שֶׁאָכַל וְשָׁכַח וְלֹא בֵרַךְ. It should say מִי שֶׁאָכַל וְשָׁכַח לֹבֵרַךְ. He explains that the mishna is not talking about someone who forgot to bentch, because that would
never happen. Rather, the mishna is talking about someone who ate and forgot - that he ate. Mimeila he didn't bentch.