Four leaf and greater are actually mutant or genetic defects presenting themselves. If you find one on a plant you're more likely to find more on the same plant as it has already presented the defect.
Not only that, but finding this many 4+ leaf clovers in a small area is a clear indication a pesticide/herbicide has been used. I used to work at an orchard that tested various chemicals and I found 4, 5, 6 and even 7 leaf clovers ALL the time. It was rather alarming.
Please tell him that
Edit: like me
He's got a green four-leave clover tattooed under his eye though :)
That's so cute!