Dude theres nothing to worry about at this stage, if there really was a legal issue you would have recieved a legal document not a dm on discord. If they had chapters uploaded on tappytoon then sure they might have been overly nice (but lets face it thats not the course of action for stolen content) and they also said they're in the "process" of getting it copyrighted so even if htey are telling the truth, 99.99% sure they're not, you can keep uploading till they send a C&D letter.
You have nothing to worry about at all at this stage. Source : i've done legal studies