BS”D
Who did he write to? TorahTrueJews or NK? If TTJ still follows Reb Yoilish ZYA’s derech then they are 100% legit.
The response looks very well thought out and perhaps our hesder Nachal Charedi sergeant baited the wrong man. (Kraus is too common a surname to ring a bell; all I know is that no one of that surname went to Iran.)
The NK website is Ku Klutz Karta and not Neturei Karta. It seems to be run by Yisroel Dovid Weiss. They even translate it into Farsi for their buddies in Iran, or at least they did a few days before Purim which is the only time I bother looking at that site.
The real NK of Rav Katzenellenbogen probably do not go online.
The only sane representation of the three oaths based opposition to tzioinus online is indeed TTJ.