I have read that the inspiration for Pooh Bear came from the pet cub that a Canadian soldier in WWI brought to England, and was compelled to give to a zoo, where A.A.Milne brought his son to see it. It seems to me that at the end of the book a remark that the name came from the toy bear having a fly light on his nose, and going "Pooh" to drive it away, followed by a disclaimer I cannot quote accurately.