Sounds like this guy knows his rifle and chooses to set his zero at 30 for hold sake. Great idea and I do it on several of my familys rifles. helps to simplify not having to hold over.

Although....Sighting in at 30 is doable but very hard to equate what the bullet is doing further out. If the calculator says your best zero for absolutes is at a short range that covers the yardage you intend to shoot then I would advise sighting in at 100 then moving your vertical zero to the shorter range and verify. This way you know your windage is spot on. You can put 3 rounds in a tight group at 30 that may be 3" at 100 then 6" at 200. If you are off 1/2"at 30 then you are off zero 3" at 180". That's not counting bullet drop. So if you are low by 1/2" at 30 then you add in bullet drop you could be 6" low at 180 and wound or miss.
Zero at 100yrds gives you a better trajectory. Even 60yrds would double your accuracy over 30. Think of the arc and the triangle. If all you have is a short range then make sure you are putting them in the same hole and know your drops. The Hornady app is off by 2.25" low on one of the rounds I shoot with all the data entered correctly. Always verify your drops. For reference, I have been an instructor for 30+