Although there may be overlapping similarities in the two behaviors, a superficial determination can be made by looking at a couple of major aspects:
A jealous bird will focus attention specifically on the newcomer, whose mere presence may trigger negative behaviors. That person, animal or object is usually the only thing attacked or reacted to, regardless of location. There may also be an increase in jealous behavior when the bird’s favorite person interacts with the trigger.
A bird that is being territorial will tend to react to or attack almost anyone who happens to occupy a particular area. This may include pieces of furniture. Some birds will exempt other occupants of the home, while focusing on visitors or new arrivals. This is not the same as jealousy, and this particular problem is relatively easy to eliminate by simply not allowing the bird to claim personal territory.