This means sticking to what you saw, heard etc., without lumping things together or including judgements.

So, if your friend and you were to meet at the cafe at 13.00, and he showed up at 13.05, there's not much else you can say about that situation. You can't deduce a motive for his being late, and it wouldn't be wise to lump this being-late together with other being-lates.

Go further. The friend showed up when the clock on the wall said 13:05; or my watch said 13:05; or whatever. After all, the friend's watch may be five minutes slow; or yours may be fast.

I suspect the bigger source of disagreement here, though, is whether 13:05 counts as "being late" for a social meeting booked for 13:00. This turns out to be extremely culturally dependent. Some cultures (and some people) value on-the-dot punctuality much more than others. To some, five minutes is a rounding error, and describing it as "being late" would be the equivalent of getting out your protractor to determine if you've been given a fair slice of pie: requiring that level of precision from someone indicates that you're either a crank, or looking for an excuse to have a disagreement with them.

So going from "we agreed to meet at 13:00; he showed up at 13:05" to "he is late" counts as a "judgement", too.