Thank you for posing the question! It's one I've been thinking about myself on and off.
My main thought was that Tomson had some demons in his human life that transferred over. Either he suffered from personality disorders or a rough childhood led him to become a jealous/greedy individual at his time of death. In both instances, the build up of bad 'karma' that Tomson created for himself did not completely consume his ghost, but it did inject itself into his new un-life.
Yet I didn't want to play a character with those traits, or at least not one that displayed them all of the time. So I thought perhaps he wasn't an overly possessive individual at first, but had his darker days. This could be particularly true the closer it came for him to pass. And along the lines of his physical appearance, to be honest I didn't want to create a monster that was similar to the description on Wiki down to the last detail. I wanted to keep the 'essence' of a preta in the form you see on the front page, but I also wanted to keep it open to interpretation for those who might be interested in a full fledged preta ghost character later on down the road.
So I guess we can say that the 'preta', while being 'seen' as an entity all by itself
within Tomson, manifested from the part of him that hungered for more in his past life. This could explain why it influences him from time to time, and it could potentially cause some trauma to Tomson himself if he ever learns/theorizes that he is to blame for his own misfortunate in this afterlife. Maybe, instead of learning how to overcome the insatiable hunger he succumbs to it? Or there is a point where he has to choose whether or not to let the hunger pull him down or to control it's drive?
I hope all of that made sense? It has surely given me some ideas to think over. And if any of it it didn't make sense, I might just need to rethink the sub-species to fit his abilities/physical appearance!
Thanks again for the question!