Guessing they are talking about construction time?

edit: Oops I accidentally misunderstood your questioning. Surely that must be miles per year.

They used miles and years right before that, so I'm not sure how it is confusing that m/yr is miles/year

"mile" is typically abbreviated as "mi".

It's confusing because the way the units are represented is inconsistent.

You find the 'yr' confusing?

No, they interchanged miles with m, and in a weird unintuitive way at that. m isn't even standard for miles, it's standard for meters, and just before that miles was written instead of shortened - it's not just confusing it's also terribly presented. At least yr is intuitive, nothing about m is easily understood even given the context (which is why so many other people are complaining about it).

Okay, though that sounds like you're actually objecting for a different reason than inconsistency.

But I will note that "m" is used in the common distance-over-time unit of mph.

That, and also m=meter, mi=mile.

Miles