Wikipedia says this about P. spinosa (sloe)
The shrub, with its long, sharp thorns, is traditionally used in Britain and other parts of northern Europe to make a cattle-proof hedge.
The fruit is similar to a small damson or plum, suitable for preserves, but rather tart and astringent for eating fresh unless it is picked after the first few days of autumn frost. This effect can be reproduced by freezing harvested sloes.
Since the plant is hardy, and grows in a wide range of conditions, it is used as a rootstock for many other species of plum, as well as some other fruit species.
I’ve made some Schnaps out of sloes before, but there is not much more you can do with the fruits. Like Wikipedia says it, this species is rather used for its quality as a hedge and as a rootstock. So not sure if one would regard it as domesticated, but we certainly didn’t domesticate the fruits into being tasty.





If you search Wikipedia for plum, it is quite clear that there are various species of plants that have been domesticated and that are considered plums.
So yes, these are different species. What the meme is referring to is probably Prunus domestica though, where Wikipedia has to say this about:
The other two mentioned species seem to have been species that we’ve domesticated on their own, without hybridization. At least there is no mention of it on Wikipedia.