Boston didn't trade for George or Butler because doing so before free agency would've made it almost impossible to land Hayward.
If they traded for George or Butler before free agency, they wouldn't have had the cap space to sign Hayward. If they were going to get Hayward and trade for another star, it had to be in the correct order.
I don't think this says anything about whether or not the decision was pre-determined. If anything, it makes it seem more likely, given that Boston was willing to risk losing the opportunity to trade for George or Butler so that they could wait until FA to sign Hayward first.
That's not true about the cap-space thing. They could have easily made the room to trade for George and sign Hayward. They literally say the reason they didnt do it was because they feared not landing Hayward.