As I explained in my previous post, Kinson came under Canford until absorbed into Bournemouth in 1865.
Because parish record books cover a number of years, one wouldn't expect them to start a new Register just because a church was absorbed into a different area. This is why Ancestry have indexed the baptism under Canford, but the image correctly shows it took place in Kinson.
It always pays to look at the actual image, rather than rely on the England Select Births and Christenings, many of which are are incorrect.