I wrote "For the ETRTO305 folding bikes, you are right they have usually a very short frame that doesn't fit for most US and European cyclists".

Usually, doesn't mean that all ETRTO305 bikes have all a short frame!

But many have a short frame because originally, ETRTO305 was a kid bike wheel size.

And I wrote ETRTO305, not 16" that cover two common rim diameters, ETRTO305 and ETRTO349. ETRTO349, a wheel size used originally for the Brompton, is mostly used for adult folding bikes (some trikes and velomobile also use ETRTO349 for their front wheels).