I’m not understanding anything out of context. I’m simply quoting Rav eliyashiv who says (by quoting the yeshuos malko) that nignaz is understood כפשוטו. This was in response the the claim that “nobody” can possibly understand נגנז כפשוטו.
The claim that the rishon as group all understand nignaz meaning something other than it’s basic understanding, is quite dubious. Be either way, I’ll Rav eliyashiv and the yeshuos malko decided for themselves whom they can argue with. I’ll simply follow 99% of contemporary poskim who for the past 15 years were simply not impressed and not convinced, that tzitzit strings dyed with murex is the mitzvah of techeles.