No, it's not sarcasm.
Only thing that I could think up is that I am tolerant of fallacy. I don't pay any attention to mistakes of others, unless I can gain something from them. If someone is being incorrect or lying of which I am aware, I don't feel the need to correct him/her or reveal to him/her I know s/he is lying. If someone told me it's not raining outside, while we both stand in front of the window and I'm looking how the rain is falling, I'll just say "Ok". I think I don't care about what people say, I only care about the actual state of things of which I'm the only one who can verify their truthfulness. If someone is saying to me it is not raining when it obviously is, I don't care about what that person said when I know he's statement is incorrect. Hm... this reminds of an idea I pondered about some time ago: do I ignore mistakes and fallacies? I think to an extent I do.
In a way, if he said that he studied Arabistics meaning for example French and Chinese, then I automatically assume he meant something else and not Arabistics, since to me French and Chinese being part of Arabistics is not a correct statement, therefore in my head I replace it with the most plausible correct one, that he either meant something else and not Arabistics, that Arabistics means something else to him than to me, or that he didn't study French and Chinese but some other languages and just made a lapsus.
The second probable explanation I think gives people the most problem, since unlike me they expect that words carry a universal meaning, like window means a window not a door, which for me doesn't matter if someone used it with that meaning. I would be like "Oh this guy calls the door 'a window'," and just go along with it.