I guess, I mean sometimes being nice is good

Arizona might not have wanted to commit to a contract and just let it be known they were willing to move him. Chances are Boston jumped on it before someone else traded for him and gave him a contract. If they waited until he was free to choose, it may have been too late.

He would have become UFA at the end of the season, so i think its way more likely arizona was informed he wasn’t going to sign with them, and the bruins thought it was worth it to get him in their system/culture earlier.

That's a possibility as well. I don't think it's worth a pick, but it's only a 7th, so it's negligible anyway.