Haven't listened to the podcast, so maybe they cover this, but when was this proposed trade offered?
To me it doesn't make sense to make the offer around the '16 draft. Not only did IT represent the team at the lottery, but they also had plans to make a hard push for Durant/Horford. No way they'd blow it up at that point for another draft pick.
2016 trade deadline? Maybe, as the team was 4.5 games out of 2nd and 8.5 games out of 1st, while only 3 games out of 8th.
2015 draft/summer/early in the '15-'16 season? This would seem most logical to me. The team was still planning on bringing IT off the bench at this point. Coming off that nice half season run, try to flip him for a draft pick a year out. Sounds like an Ainge move.