I doubt this happened.
They needed to trade Ullmark, because Swayman was their guy. They did not have the luxury to hold on to Ullmark, because the market for him was limited. Had they waited to move him, Ottawa could have moved on. The fact that Boston only got a late 1st while having to take Korpisalo should show you how limited their leverage already was.
Not to mention, Ullmark could have added Ottawa to his trade list on July 1st. This would have given him and his agent complete control over the situation, because they could have said we only want to go to Ottawa with an above market-value extension in place, or we want to play out the season in Boston and won't waive for the 1-2 teams we know wanted Ullmark that we now added to our list.
Ullmark apparently did not have Ottawa on his list because with Ottawa adding Korpisalo last year, burning a spot on Ottawa didn't make sense. That isn't to say he was upset about going to Ottawa, but it would only be logical to assume that he would add Ottawa to his list on July 1st because it would only further add to his leverage.
The short of it is that they had to move Ullmark when they did. They chose Swayman, and the market for Ullmark was limited and challenging.