Like this is not consistent with the headline.
It's also not really true. Biden has made several public appearances (he looked fine during all of them) and is going to be on George Stephanopoulos on Sunday.
"If he proves himself capable of doing so, I'll happily acknowledge error."
This is not Serwer saying he's agnostic about whether Biden will do this. It's saying "I'd love to be proven wrong, but I don't expect to be." Otherwise, no error to acknowledge.
He's on here, maybe we can ask him.