9th brigade is operating off the eastern coast.
They really shouldn't be risking the signatures of the J-20 with patrols anywhere near Chinese eastern borders. It could be nearer to India or well within China.
Plenty sure that PLAAF would have flown J-20 without LL in many operations and exercises that weren't broadcasted publicly. Maybe it's just the first instance where it has been. I still doubt this would be near eastern borders where Japanese and Americans have eyes and ears switched on 24/7 for things like WZ-8, J-20 and so on.
9th brigade is based in that general area, but that doesn't mean the aircraft operates at tactically significant distances without luneberg lenses that would be able to meaningfully compromise it.
Operating within Chinese air space near the coast versus operating in international airspace just outside China's territorial airspace versus operating deeper in international airspace many dozens or hundreds of km outside of China's territorial airspace... They're all very different.