What you are experiencing is completely normal. They will eventually shed and then re-grow in the future.
The practice of medicine, hair transplant surgery in this case, does not conform to set rules. You may be one of the few that have early growth.
Hair growing immediately after hair transplant
This is common but it is unfortunately not live growing hair that you are looking at, but rather the movement of the hair shafts within the hair grafts as they move up through the skin before shedding. Don't worry, your live growing hair will grow in 5-6 months after the transplant was done
Growth rate after the procedure
Hair goes through its intrinsic cycle of growth and in your case about 15% were in the growing phase. Yes it is normal to have some of the hairs not fall off and continue to grow. However, usually most people start seeing growth in 3-4 months after the procedure and continue to grow in for up to 18 months.
Grafts still present after my transplant
When grafts fall out too early I get worried. I never worry when some hang around longer. If grafts have enough tissue and have good oxygen supply, hydration and are handled delicately during the procedure and are given good post op care - a proportion stick around!