otos aren't plecs either. But they're still cool.
Technically, otos are plecs. "Plec" is a term that covers all loricariidae. The name "plec" comes from hypostomus plecostomoides (or plecostomus - I always get them mixed up!) which used to be our "common plec", the name stuck with all other species of loricariidae despite there being only one true "plec", so technically most of our "plecs" aren't...well...plecs. But otos are in the loricariidae family, so really just as much a "plec" as a royal, gold nugget, bristlenose, or any of our other "plecs".
Confused?