The What Lorn Done and Why:
Lorn signaled Siege to distract Neles while she jackaled on ahead of the party to find a tunnel entrance. When the party made it to the tunnel, Lorn stealthed off to the shadows to give Neles some of that sweet, sweet neck dart of
Drow Poison (which only knocks you out). Combined with the alcohol already in his system, Neles went out like a light. Siege then deposited him into an empty wine bottle. She was supposed to leave him in a full wine bottle, but didn't care to drown anyone that day. Yes, when he comes to he'll have the worst headache ever, and it will suck smashing his way out of the bottle, but at least it will provide him some shelter from creepy crawlies til he sobers up.
Lorn did this not exactly for what he said, she's pretty abrasive herself. She removed Neles from the situation because he was making everyone else tense and she didn't want Torrim to make a grand show of cleaving him, or maybe the tiefling castrating him in his sleep. Lorn has experienced first hand what can happen when a party turns on each other and doesn't care to repeat it.
But the biggest reason: he was drunk on the job.
This isn't amateur hour. They're plumbing the depths of an inter-planar dungeon built by a Demon King. She's got to be able to rely on everyone keeping their wits about them.