I very much doubt it. Chinese are fully aware of Pakistani politics and it would have been easily handled by their ambassador to Pakistan. There is something bigger going on and it must be big for the President of China to meet the generals, and it must be of a very strategic nature or serious cause for concern.
1. Most likely China have got whiff of a Hindjew prep for an attack on Kashmir
Why will be there an attack on Kashmir? You mean on Pakistan controlled Kashmir? I don't think so...Though Strike on Terrorist camps or on their leaders...is possible.
2. or it could be the impending collapse of the Afghan government and subsequent Taliban take over.
In this case, why COAS should be worried? He will be happy as this is what Pakistan wants.
3. Even worse China may be preparing to teach US a lesson in the Spratly Island conflict and is taking some of it's Allies into confidence.
What influence does Pakistan have In Indian Ocean region or South China Sea, for China to take Pakistan into confidence?.....this is absurd.
4.The fourth possibility is that there is an impending attack on Iran and Pak-China are preparing a joint strategy.
Again Pakistan is not someone China will consider to take on US w.r.t Iran. Besides, Pakistan will not like to disappoint Arab world by taking side for the sake of Iran...Neither it has the capacity to do so.
5.The fifth possibility is that there could be escalation in hostilities in Syria with direct USA-Russia conflict and China and Pak are preparing a joint strategy
Again what influence/stake does Pakistan have in Syrian conflict? For that matter even China? I don't think so.
6.The sixth possibility is China wants to ensure that their investment in CPEC is secure and are tightening up security.
What is new in this. Why COAS would be worried for it?
7.Lastly they want alarm bells to ring in New Delhi.
No, I don't think so...
My assumption:
1. Warning to COAS that if any questions are raised in Pakistan, for CPEC or what China is doing to it's Muslims etc....there will be a severe impact on relations/CPEC investment
2. China would have said that this time we won't save you if US-India-Russia etc bring anything on JeM leader in UN
3. No more further investment in CPEC till payment for previous loan instalment is received.
4. China has intelligence that US-Israel-India are planning some sabotage on Pak's nuclear assets/facilities
5. Take action on terrorists (LeT/JeM/HM) etc to please India so that India can be pulled into BRI initiatives...as otherwise, the business viability of this CPEC/BRI is not profitable. Also a happy India will tone down it's protest of CPEC passing through Kashmir/GB.