In "sensei says", the movements in kata have a certain meaning because the instructor/organisation says they have that meaning. And the meaning might be bloody good, effective and easy to apply under pressure (Or it might be in the "jumping over swords" category). It is just something that is taught. And what is often attached as technique to the kata might be attached there to emphasise a certain point and not actually be the best or only meaning for a kata that that instructor will teach if you stick around long enough (but that's another blog post).
Reverse engineering is essentially looking at the movements in the kata and playing around with them (preferably with a
The third way is "that looks like...". I've been doing this one a lot lately - "That looks like the first turn in seisan", "That looks like this bit of shisochin", "That looks like....". Meaning is ascribed to bits of kata based on the practitioner's past experiences with doing techniques/applications/fighting. This variety of meaning is personalised to the individual who has it (until they become a teacher and instruct it to their students, whereupon it becomes "sensei says").
Which is better? None of them. All of them can be great (depending on who the sensei/organisation/individual is), or all of them can be crap (again, depending on the people involved). What is important is that part of understanding the kata is understanding how meaning is derived.