It’s not impossible, but I find it hard to believe that him being the step grandfather has anything to do with this. Or that he dropped the baby out of a cruise ship window in front of many people on purpose.
I think he just made an idiotic move. Like a previous poster stated, I think he over estimated his strength, and a toddler’s desire to dangle out a ship window. The child probably had a mini freak out and that caused him to lose his grip.
I think what makes him a bad person, and not just a grossly negligent idiot, is this lie of being colorblind, not seeing that tinted windows were open, lifting baby up to bang on glass like at her brothers hockey games... He really laid that lie on thick.