Trump says he "has proof" that he didn't make this remark.  How often has he said he "has proof" of something, or  "big coming soon", yet nothing ever materializes?
What's more likely is that tomorrow he'll unleash a twitter storm on some unsuspecting target -- a restaurant that doesn't serve patriotic enough apple pie, a kneeling athlete, the French -- who knows -- and everyone will forget to ask them for the proof.