They had a point that his motion was not the fastest in the league. However, what he lacked in motion quickness, he made up for it in a big way with ball velocity. This is not to say that his motion was perfect but I don't think this was a huge deal as some reporters were saying around the media.
New Bears offensive coordinator, Luke Getsy has worked with Aaron Rodgers as his quarterback coach for a while now. He certainly knows a thing or two about quarterback play. He will be able to help Fields' motion if he deems it important to do so. Either way, I think that Fields has such a good attitude that he will be able to adjust to anything thrown his way.
Here you can see the AI version of his motion.
Check out the version in action: