Okay, so it has no bearing on D&D 5e. I figured as much.
Correct. For my part, I didn't intend the 1E call out as an appeal to authority. It's more of an explanation of how/why that interpretation exists.
As for whether or not that's a "good" interpretation, it depends. It's a pretty simple rule of thumb and not grossly inaccurate. Sure, a 160 IQ is, essentially, a 1 in 10,000 chance (top 1% of the top 1%, IIRC) while a 16 comes up in 6/216, but it's heroic, so that may not bother folks as much as having to find a way to get a 20 (or whatever arbitrary number outside the bounds of a 1 in 216 granularity) in order to play a wizard as smart as Einstein or Hawking (both of which I've seen listed at 160 IQ).
IMO, Intelligence is in a "sweet" spot (i.e. really lousy one) between, say Strength and Charisma for purposes of measurement. Strength is relatively straightforward because its mostly a measure of how much a person can lift. Sure, you can argue about whether a bench press, dead lift, or drag is the best measure, but it's variations on a theme. As a bonus, there's no clear, easy equation for mapping Strength to, say, bench press. Charisma is purely subjective and there is no real-world value to which you can tie it. A higher charisma means you're more influential, likable, or something; there might be disagreement, but everyone knows its all arbitrary. For Intelligence, we have IQ, which is a real-world number and deceptively close to 10 x Int, including having a mean just above 10 or 100. But, the percentages don't break down right (see above)
and there are parts of the Intelligence stat that don't map to IQ: memory, deductive ability, creativity (or is that Wisdom? maybe even Charisma), etc.
