It is also the most logical and the only 5th Gen option available at this stage. KAAN has not entered serial production for domestic induction, let alone for exports. It is also, as yet, reliant on an American engine, which may not be approved for re-export to Pakistan. J-35 would require significant internal infrastructure development, but it would still be relatively easy to incorporate it into the PAF's existing Chinese-origin ecosystem compared to KAAN.
Also, service chiefs are not needed for formal negotiations. That is usually a government-to-government formality. That said, there is nothing to suggest a deal on J-35 would be concluded during PM Sharif's ongoing visit to China, and there is nothing to suggest that it won't be. Given previous trends, particularly with J-10C, one shouldn't be surprised to learn of the deal mere few weeks before the jets land in Pakistan.
Finally, all hints are pointing towards J-35. KAAN is being closely observed but doesn't appear to be on the menu yet. If J-35s are inducted, KAAN's prospects would become very difficult.
Note: CDF Asim Munir is now in China. He is a de facto boss of the air force as well.