Ok, a few things.
Nearly all small engines require Regular 87 octane. There are exceptions, but most small engines don't run a compression ratio higher than 9:1. Some can be as low as 6:1. Of course, combustion chamber design plays a major role in necessary octane rating, but in general small engines are not high performance machines and do not require high octane fuel.
The higher the octane, the slower the fuel burns, and the less heat produced. Fortunate, they formulate all gasoline grades to be within 2% energy content of each other. However, this is why you aren't supposed to run premium in an engine that only requires regular. It can cause carbon buildup with an engine that only sees light duty service.
Everyone has their things. Fill it up with whatever you want, it's not like he's going to know the difference. He probably uses Marvel Mystery Oil in the crankcase also. *shrug*