Presumably, Thailand has an Embassy in China staffed with educated people who can inform the government officials in Bangkok of the state of current affairs in China. Even if one doesn't have first hand information from the embassy in China, the internet is a wonderful source of information. Of course, you can't believe everything you see on the internet so some basic cross referencing and critical thinking skills are required.
Given the information available, it would seem to be quite naive to base one's hope for tourism revival on China. The economy in China is imploding. Unemployment is rampant in all demographic groups. Major cities in China are facing possible bankruptcy. The Chinese government is confiscating passports and discouraging tourism abroad to stop capital out flow. Additionally, Thailand and it neighbors, especially Vietnam, have benefited from major businesses relocating from China.
All of this, and more, is open source information. I speak with people on mainland China daily and consult with companies seeking to relocate outside of China. This is not a conspiracy theory or rumor.
It seems to me to be the height of pure folly for Thailand to base its future tourism hopes on China. A better approach would be to focus on domestic tourism, near shore tourism from other SE Asian countries and distant tourism from Europe and North America.