The tweet mentions that in order to trigger XSS, the WAF had to be bypassed using unknown techniques. This highlights a potential vulnerability in the WAF provided by PortSwigger. A blog post should be created to discuss the bypass method, the impact on the WAF, and steps to mitigate such vulnerabilities.
For more details, check out the original tweet here: https://twitter.com/drak3hft7/status/1834120948762509574