I can guarantee it isn't purely Richmond green. For starts the Richmond green is very fuzzy, and this is spiny. Secondly the Richmond green tastes like a watermelon or apple and this one tastes like a cucumber.

Hi. I'm sorry if you don't agree with my identification, but the reasons you describe are not strong arguments against it. In terms of taste, I can find no information describing Richmond Green Apple as tasting like a watermelon or an apple. For example, this site in Australia (where the heirloom variety originated) describes it as "crisp, white flesh that is incredibly juicy with a refreshing tang. None of the bitterness in the skin other types can have." The apple in the name alludes to its appearance, not its flavor. For this reason, you may see the term in quotation marks in descriptions of the fruit, but that doesn't mean it tastes like an apple. It tastes like a cucumber. In terms of the spines,  both pickling and slicing cucumbers naturally have spines, as described in this article from Mississippi Sate University, so that is not a feature unique to spiny varieties (or necessarily absent from varieties such as Richmond Green Apple). I also found no descriptions of the variety as "fuzzy", which would be very strange for a cucumber. This article from Iowa State U. discusses hybridization in cucumbers. It notes that any hybridization that may occur will not affect the year's fruit. The sole exception are specialized gynoecious hybrids, which does not include any of the varieties you planted. Therefore, this cannot represent some unusual cross, unless it was from two varieties that you planted last year. Unfortunately, the only way to know for sure what variety it is would be genetic testing to compare it to a known plant of Richmond Green Apple, but that would be cost prohibitive.

Right but the Richmond Apple Cucumbers that I know I grew didn't have spines.  They were fuzzy and spineless.  And they don't taste the same as the ones I know were Richmond Apple Cucumbers, which had a fruity taste rather than a Cucumbery taste.  If these are traits which are recessive, then the original seeds wouldn't have had them, and any self fertile offspring would be homozygous for those traits.  And maybe they aren't but it seems weird that the characteristic traits of a Richmond Apple Cucumber would be absent.