There are definitely two possibilities here:
#1: The Cavs liked Thompson all along, and everything involving Jonas was a ruse. I'd be tempted to say that there was also a possibility that Kanter was the main target and Thompson was the fallback. We know that Thompson was a special defensive big at the collegiate level, and he can be a fast break basketball role player at a high level. I wouldn't rule it out.
#2: The Cavs tried to get too cute and draft for another team, knowing that Toronto liked Thompson. I always thought Thompson was a great fit replacing Reggie Evans in Toronto. I guess that if the Cavs wanted to get cute and play games with Washington, they were also comfortable with keeping Thompson if it blew up in their faces.
No matter what, I'm far more concerned with the Cavs' pattern of treading water in the late-first and early-second. Grant keeps walking away from the craps table when the sure-thing is gone. The big winners in this game still roll the dice and win when the chips are down and come out winners. I don't know if Grant has that type of personality, or those type of scouts.