> from 19th-century horse-racing slang

There's hardly any worse "source" for etymology than that kind of jargon.

> "ringer" was a late nineteenth-century term for a duplicate, usually with implications of dishonesty, ...

Is that it?

> Hope this helps

Not in the slightest, no. If anything it confirms my bias that editors are gullible.

Which, to get back onto topic, would mean to think that the motivation was not exactly what is reported here, but something come a long way.