This relationship between the dragons makes a weird kind of sense.
I'd imagine one of the worst things godlike immortal beings have to deal with is sheer boredom. So randomly pranking/attacking each other to stave that off doesn't seem that odd. The line between being a friend or enemy would be as simple as what Kalavis said near the end, making sure the other person wouldn't die as a result.
Also wish Kalavis would stick around, she was cute. I imagine the shenanigans between her and the lamia would be pretty entertaining.