Is there a word for a comment which makes no sense or adds nothing to the current discussion?

Consider this conversation:

John: I am giving free chess lessons.
Mary: Nice! You’re a true teacher.
John: How so?
Mary: A true teacher imparts knowledge without a price tag.
John: But what if teaching is his only source of income? Would he not be a “true” teacher then?
Mark (in response to the question above): You clearly mentioned “free chess lesson”.

I don’t see how Mark’s comment adds anything to the discussion or makes sense in the current discussion. It is “redundant” — that’s one word for it — but is there a more fitting word?

The best I can think of is "non sequitur," which means a conclusion or statement that does not logically follow from the previous argument or statement.

Also, maybe it is a boondoggle (Work or activity that is wasteful or pointless but gives the appearance of having value).

Otherwise, it is picayune (worthless, petty).

I'd go with non sequitur.

I think superfluous might do the trick.

superfluous: not necessary or relevant; uncalled-for (...) serving no useful purpose; having no excuse for being;

Source: The Free Dictionary.

non sequitur (OK, 2 words), off-topic, irrelevant, ..., depending on the context.