A player's position is determined by their current skills, and can change when a player's skills change. Your player must have had a skill change at the training update that shifted his suggested position (I suspect a Jump Shot increase, as Jump Shot is highly weighted for small forwards, but it could have been something else). In fact, it is possible to have a player shift back and forth between suggested positions regularly, if you have a player with a mix of skills that is weighted fairly evenly at each position (by whatever determines suggested position).
The transfer value estimate changed as he is now being compared to an entirely different set of players who have been transferred recently. Note that this is just an estimate, and is based on other players. The amount that your player would actually sell for should still be similar to before the position change.
Also, note that his suggested position has no impact on his performance on the court, so nothing to worry about there.
I hope that helps :)