Bourne is the best WR on the Patriots. Obviously other teams think the same. I can't imagine Bill would be that dumb or overconfident to trade him away.
Guessing these are probing calls being made. Teams know the Patriots like to trade guys in their last year when they don't think they'll resign them (not saying that's the case with Bourne yet, necessarily), and there was some friction the year before. Add in that they're keeping both rookies, and I'm sure teams are just seeing if they can buy low. I doubt the offers were all that high, and I'm glad he's staying.