Is the solicitation challenge letter just a response to the questioning company

Yes. According to the query of China's procurement network shows that the tender challenge letter is only replied to the questioning company; the tender challenge letter is filed by the questioning company, and before replying to the tender challenge letter, the bidders should read the tender documents carefully, understand the conditions and requirements of the tender to make sure that their responses are reasonable and well-founded, and submit them in the stipulated period of time.