As the seller it is completely your choice as to who you want to sell to. You have the right to make that choice no matter the circumstances. Sure you could have let him know sooner- so what. You could have even waited later too but you didn't. Props to you for not only posting this but for also being willing to send the guy some money to recooperate the cost of the riding gear he bought.
Honestly in my own opinion, I think he should have waited to buy the gear until after he had received the bike, then again he may have found a great deal and didn't want to lose out on it. You went out of your way to try and make things right with him by sending him money. There should be no shame in this post. Understandably he was probably upset but, hopefully he wouldn't come out on here and bash you. That would be very immature. It's your stuff- take the best deal out there.
Rep awarded for this post.