A quick question: why these aircraft fly with drop tanks but no weapon?
1. Live weapons are threatening. We all know how much the western media loves to spin and distort any and everything to make China look like the bad guy. There is no need for China to give them more ammunition.
Armed patrols will just have the usual suspects making a big song and dance about supposed Chinese "aggression" or "bullying", and the western media will just lap it all up.
2. No operational need. There is zero threat, so why lug live weapons around? Those are heavy and draggy (so costs a fair amount of fuel - ie money and time on station), and the weapons themselves only have a finite useful life when carried on missions. Better to save that for when you actually need live weapons.
This is just a show the flag patrol, the idea is to be there and be seen to be there.
3. Flying unarmed could arguably be seen as a display of dominance. By flying unarmed in the area, the Chinese are in effect saying that they are safe without even needing to defend themselves.
It is potentially a more powerful psychological blow to opponents' moral than a fully armed flight making a pass over.
If you see an armed patrol by a much more powerful opponent, you can sometimes get a moral lifting boost from showing defiance, that you are not intimidated by such a crude show of force.
If you see the same powerful opponent send in unarmed planes on patrol, you don't get so much of a "defiance boost", as there is little threat, and you could feel like they opponent just doesn't even see you as a threat worthy of them having to pack even self defence weapons, which could be a big blow to egos and troop moral.