If an instructor is carrying out dual instruction (and is therefore PIC) with a PPL or with a student - providing there is no one else on board - he is not flying with passengers.
In theory, that instructor could be way past 90 days and still be legal. Doesn't make it right of course.
Now look at the Instructor requirements to teach the Night Rating
(e) the night rating, provided that the FI:
(1) is qualified to fly at night in the appropriate aircraft category;
(2) has demonstrated the ability to instruct at night to an FI qualified in accordance with (i)
below; and
(3) complies with the night experience requirement of FCL.060(b)(2);
So to teach the Night Rating with no passengers on board the FI must be 90 day current.
No doubt unintentional; a typical case of poor drafting and even poorer checking.