Absolutely insane. And i say that as someone who grew up on a farm with shoots. Feeding a pheasant is like feeding any other bird, it is no big deal at all. No one raises hundreds or thousands of horses or ponies and then just lets them go. A persons horse or pony are very important to them, the pheasants are not given a shit about by anyone apart from to make as much money as possible. They could not be more different.
They are not a wild animal, they do not have a natural life and do not have the instincts to be able to survive in the wild. They are as stupid as anything. A quick google says that:
Predation: Before the shooting season begins, 23–25% of released pheasants are predated or scavenged, usually by foxes. During the season, 13% are predated or scavenged.
Disease and starvation: Many pheasants die from disease and starvation before they can be shot.
Vehicle accidents: Many pheasants die from being hit by vehicles.
Other causes: 14% of released pheasants die from other causes.
Unsold: Millions of pheasants are killed but go unsold and uneaten. They are then buried, incinerated, or fly-tipped.
Wounding: Up to 40% of birds are wounded instead of killed.
Lead shot: Toxic lead shot is used to kill the birds, which harms the environment, other animals, and people.
The pheasant shooting season in the UK runs from October 1 to February 1. Around 47 million pheasants are released each year on shooting estates, mainly in England.
Feed the bird OP, but expect it to become reliant on you as it will have been fed all it's life until it was released to be shot.