This would be credible if they didn't constantly use those Salafi populations abroad to promote their interests and to counter other regional powers and undermine rivals. Salafists in Iraq were constantly antagonizing and destabilizing any Iranian influence in the country. In Syria they were used to undermine and eventually overthrow the Shia-friendly government. Throughout West Africa Salafi groups regularly compete with Iranian-backed groups for influence. And the main reason that the Uyghers are in camps and the Hui are not is due to their Salafi-jihadism and terror attacks being viewed as the Chinese government as an attempt by foreign powers at interference in their internal affairs. These same Turkic-Salafist groups were seen in Syria fighting on behalf of the Islamic State, and they largely displaced the Turkey-aligned Turkic nationalist groups in Xinjiang, allowing Saudi influence to shoulder aside Turkish influence in Central Asia.
This is an interesting in-depth rundown of the history of that conflict and present conditions:
https://mesbar.org/salafism-china-jihadist-takfiri-strains/
What you see again and again and again is that the leaders of these movements go to Saudi Arabia on Haj and come back preaching Salafi Jihadism. Of course the Saudis themselves wash their hands of these groups and act as if they have no relation, but I think it strains credulity to think that the concurrence of both Saudi interests with the actions of these groups and the timing of these trips is all just some bizarre coincidence.