Good question. The folks I've discussed this with and I have several different possibilities for what was going on there. Here are a few of those...
1. Mana's soul was drawn from the Earl and not from "Heaven" or wherever they're normally supposed to be called from in the DGM world. The rest is more or less as we know it from the manga backstory.
(**Actually, it might be nothing, but notice that in page 16, there's a very odd colour-negative image of the Earl in the middle of Mana's rage/woe-filled yelling at Allen? See it, with musical notes above his head? Every other image on that page looks normal and not distorted in any way, but for that one panel he looks very strange. Could that be a hint?)
2. Mana really did die (as a regular human) and his soul went wherever they go in DGM, but his body was "kept" by the Earl. When Allen called Mana's soul back, it messed with the Earl and Allen got cursed.
3. Allen's memories are either partially distorted or not at all reliable. (Actually one of these might be the case either way, seeing as it is implied that Allen is forgetting/misremembering something both by Nea in chapter 198 saying Allen and the Earl are "broken" or "mad" (depending on translation-- I'll have to check the Japanese at some point) "dolls" and by Allen nearly turning into Nea right before Apocryphos first attacked him in 203, just because he wondered if something would "change" if he remembered.)
There are more theories but I'll just leave it at that for now.