Could be the first shipboard arrest landing trial of JL-9GJ, "J" normally indicate the aircraft is based on a ship (Huitong's remark refers).
Example of suffix "J" letter designation is Z-8J. "J" is for Jian or 舰 ship in Chinese. JL-9GJ is the latest variant the gained much publicity a few months ago, though no photo of one with arrester hood was shown.
Navy aircraft that is not based onboard a ship normally gets an "H" or "Hai" for Sea or Navy (Haijun) in Chinese. Ex J11BH. They are not given the "J" suffix.
This is not a strict ruling that the PLAN is adhering to, as can be seen on J15, Z9C/D and H6J. However in JL-9's case, this suffix has some significance to it.