From what I understand, Love can't sign an extension right now. He's under contract for 2014-15 and has a player option for 2015-16. It's not until next season that he could sign an extension, right?
My info is based on comments on this forum, but from what I understand, a team that trades for Love could make the trade contingent on Love opting in for that 2nd season. Since he can't sign an extension, getting him to agree to opt-in for year 2 is the best any potential trade partner can hope for.
It could still end up being a risky 2 year rental, but at the very least you'd have a bit of a buffer... worst-case scenario if things aren't working out, you could just explore trading him next summer (since he'd be under contract for another season).
So my guess is this Boston trip was related to that opt-in. Love may have told his agent that there were a couple teams he'd be willing to opt-in for (such as the Lakers). But perhaps he was on the fence about Boston. He doesn't really know the city and hadn't visited it before. They set up the trip a couple weeks ago. Love has been in communication with Rondo and they made sure they were both in Boston at the same time. This was likely just an exploratory trip set up by Love's agent. It gives him a chance to feel out the city, contemplate the Celtics and see if he'd be willing to opt in for a 2nd year upon being traded there.
That doesn't mean the Wolves will trade him. That doesn't mean the Wolves will trade him to Boston. That doesn't mean Boston even has the best offer. But assuming Love and his agent give the green light on opting in for that 2nd year, Ainge could feel comfortable offering up assets without worrying about it merely being a 1 year rental. The more teams that Love is willing to do that 2015-16 opt-in for, the more teams the Wolves can negotiate with over the next months. If Love decides that he doesn't like BOston and isn't willing to commit to 2 years there, Ainge doesn't really need to waste his time... because he knows he'd be more than likely just getting a 1 year rental.
This is still probably a long way from being over, though. Other teams will have competitive offers... and maybe Love decided a while ago that he was comfortable opting in for some of those teams.