Maybe we can set aside the weight issue for now, considering the injury and the fact that Yab hasn't been on an NBA training program...ever. His conditioning in September will tell us everything we need to know.
I watched the highlights and some of the game, and it also looked like he was adjusting to the pace of the game (for a number of reasons, probably). His passes were generally pretty accurate in China from what I have seen, but here they were off. He also seemed to be in the "I can just go up and overpower people" mode - again, an adjustment period there.
Yab's also a smooth player rather than someone who gives you "wow" moments offensively or defensively.
I was trying to think of a comp and thought of Ryan Gomes. Gomes has a better midrange shot and gets his shot off quicker, at least at this point in his career, and Yab is a bit bigger, but there are some similarities, especially if you think about how Gomes played earlier in his career.