So-called 27.5" tyres are closer to 700D than they are to 650B.
This all just reminds me of when I needed slicks for the 29'er. Found 700C x 40mm tyres online, arrived as 28x1.75" and then put on a 29" rim.
Bloody stupid 'standards'.
Also, if everything else on a bike is metric, why the hell are we still dealing with wheels & tyres in imperial units? Even the chainstay, hub, spokes, nipples and axle are all in metric, and I even buy my rims on ERD in metric, yet it's an imperial sized rim with imperial measured tyres.
WHY. We even went and introduced a whole new size of mountain bike wheels (I know, not new, but mass-market new) with 650b, but Giant insisted on calling it 27.5 because Fuck yo couch.
/Rant.