While I'll disagree about Bjerg being overrated (I honestly think he's the best technical mid laner in NA), I do think he played Ezreal pretty weak. He always used his Q before his W when using both, which negates the obvious advantage of getting a whole second off of your W cd, he fired his ultimate in fights in plain view of his target which meant they could dodge it, and he really just didn't make the most of positioning with his E. There's all sorts of tricky plays you can make with him that Bjergsen just didn't take advantage of. I suspect that picking up Ezreal was a really hasty decision of his. It's as if Friday morning he found out that it was a thing and rushed to practice a couple games before deciding it was overpowered enough to justify not having practiced it enough. As a long-time AP Ezreal player, it was honestly painful for me to watch one of my favorite players not play the champion to his full potential. The only reason it seemed impressive was because he landed a few long range ultimates once he got extremely fed.
Please be aware though, AP Ezreal is very difficult to play. An entirely skill shot kit that punishes you pretty badly for not making the most of every shot is just going to be tough. The problem is, Bjergsen should have been able to make the most of it. And it irritates me that AP Ezreal will probably get nerfed in the next patch because it doesn't fall in line with Rito's status quo for their LCS meta, when in reality it's on a pretty average level for 95% of the player base. Champion Diversity my ass.