His fielding at 2B early on certainly shows he needs more experience there. Besides the ones you mentioned from last night, there's also been some poor throwing accuracy at times, and his tagging is not great. He also seems to lose focus at times defensively and as you pointed out, he's out of position or just hasn't covered the base at times when he should have.
As much as I do think he was sent down because of service time, he does need to work on improving his defense.
He has shown the range and hands to be a very good second baseman, so I don't see anything that won't improve with experience.