If they were asked, they'd hesitate in saying they didn't. Asgore died, and Flowey killed him, but the guilt that they fought him to the point Flowey could even do that...it feels more or less the same.

"Yeah. They're usually human, too, but one's a weird deer person an' another's a ghost." (Frisk doesn't sign for 'deer', since they don't know that one.)