That image you posted still shows daylight between ground and the ball.
I actually remember a situation during one of the ODIs where Bangladesh took a run when the ball ricocheted off one of their bats while sliding for the crease. Tamim has also been doing stupid ████ at the non-strikers end etc.
Shakib looks straight behind him when he edges it and SEES the ball go into McCullum's gloves. McCullum's gloves are so far in front of his face and he probably closed his eyes as you do when you're going forward at a ball, he wouldn't have known.
Tamim doesn't stand around and walks straight off. If the ball bounced he woulda seen it. He didn't, the umpires didn't and the other NZ fielders all went up as if it was a sure thing. Either good acting or else it was actually a pretty clean looking catch. You see players, keepers, outfielders etc. take catches like this all the time and they never know whether they've caught it or not. McCullum whether he was sure or not appealed for the caught behind by raising his glove in the air. McCullum is fully within his right to appeal if he's unsure, the umpire lifted his finger and the batsman who was fully within his right to a) stand around and ask the umpires to check the catch or b) even review the decision if they said it was clean. Blaming McCullum or the NZ side is bollocks. Blame Shakib or the non-striker and probably most of all the umpires. Umpires generally will always go upstairs if they're unsure on a catch. They didn't so it must have looked pretty clean.