Or it could be a murderer imagining his victim forgiving him.
He knew that his dad forgave him. In TFA Han put his hand on Ben's cheek *after* he was stabbed.
I'm on the "memory" camp. I don't think Han was ever there.
Yes that's the common consensus. However more fuel for the "Han's spirit" interpretation is provided in TLJ with Luke saying "If you strike me down in anger, I'll always be with you, just like your father." That very much paralleled Ben Kenobi's last words to Vader, who *did* become a ghost.
"No one's ever really gone" also indicates that Luke might have learned that Yoda's "luminous beings" speech really did apply to everyone.
Again, take whichever interpretation that makes the most sense to you but it is more food for thought.