As I understand it, a “weapons lock” is mostly about deliberately pointing your detectors at a target. The target may notice a spike in radar sweeps but they don’t actually know what the other vessel is doing with that radar information.
It’s kind of like when someone starts staring at you really hard. You get a feeling that they’re probably up to something but you don’t actually know if they’re coming to take a swing at you or if it’s just RBF.
From what I’ve read it’s something that happens fairly regularly. If you want to warn an other military vehicle without escalating to warning shots you flash some targeting sensors at them.
My guess is that the fighter and bomber were targeting each other and that a bunch of land based radars on the Chinese coast joined the party too.
edit: looks like I was wrong en.wikipedia.org/wiki/Radar_lock-onIt seems that “lock on” as we know it from movies and video games isn’t a thing with modern military equipment. I suspect the signal intelligence folks still have some thing that tells a pilot, “data suggests that someone may be planning to shoot you”.