In my modest opinion it is not natural behaviour. I'v heard about people who got involved in occultism and were proud of forcing animals doing strange behaviours. God doesn't teach pigeons to do such acrobatics. Let's stay sharp.
I'v heard a story about possesed person who in front of friends boasted impossible tricks, also on animals. I remember he (or she) said about a duck in a park that did something impossible for a wild duck, or any duck. That's why I see in this pigeon backflip something that crosses far beyond its natural behaviour.