Dr's confuse me

I had my perinatal appt today for my 28 week mark.

Baby Isaac is weighing in at 2lbs 8oz. His growth is perfect. 😃😃 He also said that there is nothing to worry about. For me being a diabetic the doc says everything is amazing.

BUT his growth is only in the 27th percentile. The perinatal says there's nothing to worry about unless he drops into the 10th or lower. How could he be greatly proportioned and growing properly but in the lower percentile at the same time??