If they are simply filtering out based on signs of AI, then there is no lie.
If they are explicitly asking “was AI used” then yes, there is a direct lie involved.
If there is no explicit question but you are including “lies by omission”, then be aware that there are many things people choose not to say that they would be unfairly judged for if they did state (gender details, certain parts of their history, etc) so that might not be a line we want to draw.
I'm not exactly pro-AI, in fact I'm avoiding it in DayJob to the point where I expect at some point I'll be given the choice “get with the program or leave” (I plan to leave at that point, preferably by my own choice though we'll see how heated the discussion gets!), but if there is a at least one human at the end of the process that is properly testing and cleaning everything up so there can be nothing problematic in the AI output that survives, is that really practically any different to a fully human created contribution?
The problem with AI contributions in the vast majority of cases is the lazy ones, especially considering the sheer number of them. Using signs of AI as a code/documentation smell when it comes to filtering contributions is fine, especially if you have up-front requested no such contributions be sent. Permanently blocking people who have sent obviously AI-generated contributions previously despite you asking them not to, is also fine just as blocking people who have sent in entirely human made contributions that break your other requests/rules is. But banning all AI use when if you can't tell if a good contribution did or didn't use AI aid somewhere in the process, is both a daft extreme and actually impossible (if you can't tell, how do you tell?!).