Loosey goosey instructions like that lead me to think it's not that important. And he gives you measurements, 7/16ths thick one drill bit below an 1/8th (I guess a mm), and a popsicle stick is about a 1/2" wide. Don't over think it. Put away your micrometer. I'm sure the whole thing becomes "fiddle with it till it sounds good".

Fucking 7/16. Totally normal way to measure stuff right people. Yeah just gimme that 17/32 drill bit please.

Statements dreamt up by the utterly deranged

For the record, the reason they say that is because many ocarina makers just use a popsicle stick to make the airway of their ocarinas. The exact width of the airway is actually less relevant than the thinness of the airway, as well as its connection to the fipple (the sound window). No need to make precise measurements with fancy instruments when a popsicle stick works just fine.

Source: was an ocarina collector for many years, am generally familiar with how clay ocarinas are made