“they’re going to parse it to claim he lied when he (Barr) said he was unaware of the (Mueller) team’s concerns when he had read the letter.”
The actual question was, do you know what they are referring to, when they say...
No, unless you are are a mind reader, you don’t know what someone else had in mind. In Barr’s very next sentence, after saying he did not KNOW, he did accurately summarize the concern expressed in the Mueller team’s letter (which he could SURMISE, that they were referring to).
If he did say that he KNEW what other people had in their mind, then Democrats might accuse him of lying about that.