People losing their past memories after a head trauma is fairly rare, but losing immediate memory is the norm. The most likely situation would be Pekka not remembering anything after the approximate time he left his home. Seppo doesn't expect Pekka to ever remember what happened right before being knocked out, and if effort allows him to remember a few details of hte way up... well it's pretty useless.
Aww, that embarrassed look Pekka has in the last panel is really well done. =)
He's about to say something really embarrassing, indeed!
But how are we going to know why it happened? I MUST KNOW
PEKKA use your leprechaun powers to REMEMBERRRR
If he remembered those last seconds, he'd know "I did nothing wrong, that troll had something to tell me, I better return," instead of "I must have done something wrong, better be cautious and think twice before returning."
But why? Ah that happened out of his sight, he never knew it!