First off - I am hardly a "shark whisper". What I do have is Information about keeping sharks. I have spend more than 14 years of talking with hundreds of people who personally kept these sharks in both public aquariums and private aquaria. Some of the more successful individuals report keeping these sharks for 10-20 years. And their personal experiences often backed up with all of the countless hours of research I have done on keep sharks.
Now - how can a 1.5-1.6 meter long whitetip reef shark be kept in a tank/pond that would be too small for a 1.5-1.6 meter blacktip reef shark. The simple answer is that it has to do with the nature of the shark. White tip reefs are one of three species of carcharhinids which are NOT obligated ram ventilators. Or in more every day English - that means they do not need to swim in order to breath, like species such as the blacktip reef. And for the record - whitetip reefs have been kept and even bred in pools, with a footprint of only 200-300 sq. feet.
As for the calling keeping swimming sharks like these "insane". Well - some would call the keeping large constricting snakes like mainland Burmese & Reticulated pythons, or giant monitor lizards, or venomous snakes (vipers, cobras & such), or even big cats (cougars, leopards, lions & tigers to be insane. And yet it has been done all to often. While some cases have ended badly for either the animals or their caretakers. There quite many who have been successful kept with these animals. The same is true with swimming sharks - if the person has the experience, a large enough tank, and a large enough annual budget to correctly care for them. Now I am not saying that keeping swimming sharks is recommended or advisable for 99.9% of saltwater aquarists. Because they are NOT. Any more than keeping giant constrictors, giant monitors, or venomous snakes is suitable for 99% of private reptile keepers.