1) Why are so many otos identified as "Otocinclus affinis". Beats me. Possibly they really mean something like, say, Otocinclus sp. aff. vittatus (meaning "this is a new species of Otocinclus which seems closely related to vittatus"), but more likely they're following some book.
2) Your fish is not a macrospilus, on account of it having a contiguous lateral pigment band, but other than that I can not say.
I had an Oto like this I got with some other more "common" otos, the main difference I was able to see was the large eye, and it seemed to be nocturnal. I think they are labeled as affinis because they are all caught and shipped together, and 99% are affinis.
The Otocinclus affinis on Planetcatfish picture is the right species, although it's either dead or scared. It should have a very narrow unbroken black band along the side. You can see it if you look closely, but it's very pale. The golden gleam is however typical of the species.
For what it's worth, it seems as though O. affinis is very rare in the trade. I've never seen a real O. affinis for sale.
Incidentally it's the much same with the OTHER name commonly tacked on otos: Otocinclus vestitus. Pretty much no fish sold as either O. affinis or O. vestitus, are.