Yeah, it deals 1, then remaining HP after the 1 damage. I should have spoken more clearly. I personally think it's a rather interesting way to do things, definitely easier to code, and a thing that not many people would notice or really care about.
This actually has an implication about Death Mark that I rather like. Actors in the game can't influence DM's proc chance, and while this may seem like a no-brainer, this is usable as proof against anyone that thinks that DM is "rigged" or something.
If it were possible to manipulate Death Mark in-game, which would be required for it to be "rigged" in any way, then the devs would have just made it place a death mark that instantly triggers on itself. But that would require a lot of messy code and be overall not worth the time spent on it.
So, instead, the Bombot is coded to deal one damage to itself, run a check to see how much armor it has, run a check to see how much health it has, add the two values, then deal that much damage to it.
Sorry for the textwall, but I always liked Bombot and the little peek under the hood it gave us.