My take on this is that it isn’t an issue of whether you can discuss truth or not, but rather if it’s philosophically relevant to the conversation. What I mean by that, and what I think the article means, is that the person isn’t questioning the meaning of truth really but instead avoiding the discussion going really any further by throwing out a catch phrase which is pertinent in a very distant and vague sense, but the person has no real intent to go into it.

It’s sort of seems like a form of “whataboutism” where somebody counters a point by going “Yeah but what about truth?!” It effectively ends the conversation because it’s not a matter of agreeing on the meaning of truth in the context of the discussion, but more of a distraction which can never be fully answered which stalls the original discussion.

Maybe in context those specific definitions do matter and should be stated assumptions, but often I don’t think they are. In addition, it truth or morals can’t be pinned down in centuries of effort, how could they be in these kinds of conversations? I don’t believe they could.