Other countries have vastly different statues, and in some cases true statements of fact can be defamation (if they were not widely known, I believe).
You could call out Lord St. Buggering-Little-Boys, complete with films, DNA evidence, and witness testimony, and still lose (and be on the hook for legal fees).
If I were Neimann I would actually sue now.
He hasn't said anything beyond provable facts, and let people read into his actions what they want.
Suing someone for defamation because they resigned to you in a tournament is going to be a pretty high bar.
Plus, a very strong implication thag he did so at the Sinquefield Cup.
Neimann may have something.