I saw that as well, not sure if it was a scowl, but Cruz certainly did not say anything. Since Fox News has had such long knives out for Cruz, my first thought was that it was staged...that FNS had shut off the feed to Cruz so he did hear Wallace and did not have a chance to say goodbye, making it look like Cruz dissed him? Did you notice that they cut back to Wallace and he moved his eyes off-camera for a moment...that was strange as well! From my experience in watching Cruz on TV, that behavior, a “scowling” non-response, was so out of character for Cruz...he has always been very respectful even when the interviewer has been a POS like Wallace was that day!
Pretty sure the non-responsive scowl by Cruz was real, he would know if FOX doctored it if he did respond at the end and that what probably piss him off to no end.