Memory lost/amnesia. When lost memories return, people sometimes pick up where they left off. That's the normal case. In DGM world, a lot of things can happen, from trauma to magic.
And Mana was not in his right mind.
Mana had not amnesia in that moment, he lost it sometimes (because his brother death, and maybe because the Earl pressing him too), but he had not amnesia in that moment... He does have after the incident with Red in the circus, but (logically) the incident happens after the first met, so not.