but then everything changed
Yes, I think that guy just got unlucky with the short 4 day trip. I just returned 10 days ago from a 30 dive trip there, and there were times it was feast or famine. I had a couple strings of 2-3 days where I just didn't see anything big at all. Then other days it was sharks, eels, rays, turtles galore. Overall I don't think it was much different than other times I've been there, and of course the reef has its seasons for stuff - I only saw one eagle ray on the whole trip, but if you go in late winter / early spring they can be everywhere.
If you're only there for a few days I can see how you might just miss those jackpot dives. But I thought everything looked really healthy and definitely had my share of "I saw all the things!" dives.