Far from being an expert, but maybe I can help you understand.
Teddy's consume action doesn't deal any damage since it instantly kill the target without triggering any demise effects (demise is a trigger usualy done when certain models dies and have different effects). This part is similar to the execute trigger that some models have on certain attack actions (Bayou Gator for exemple).
Returning now to Teddy's consume heal effect. The health Teddy seems to gain looks to be equal to the current health of the target since it does not specify target's max health. I know Teddy has a great pool of self-healing abilities (Regen +1, heal on Heavy Claws trigger, I've got your back trigger and Consume). The rules like Solkan state says that a model have a maximum health stat and a health stat. The simple health stat is use for the current health. It is like health/maximum health like in video games. A basic exemple would be something like rpg where you have your health bar with two number. Your health on one side and your maximum health on the other.
I hope my explanation were not too confusing.