Could there have been another cherry tree somewhere in the vicinity?

It is sometimes possible for flowering cherry to pollinate cherry trees. There would only have to be one other tree somewhere in your neighborhood, but I know cherry trees are extremely uncommon where you are.

I also had a theory a while back that it might be possible for other stone fruit species to be able to pollinate a cherry tree for the purposes of causing fruit to form.

Stone fruits - can different species pollinate eachother?

Oh, by the way Tim, I have found that down where you live cherry trees grow better in partial shade, at least the younger trees. In Winter it helps them accumulate more effective chill hours, and in Summer it helps prevent the foliage from getting baked in the hot sun. San Diego is really not a naturally conducive climate to growing cherries, but it can be done, and the climate does at least offer some unique positives: long growing season, plenty of sun means the sweetness of the fruit is at a maximum, sunny dry summers means there is no risk of fruit cracking, dry climate means almost complete lack of fungal disease.

Thank you. These trees as with all trees I have grown. Have to prove themselves. I like cherries, as soon as I saw they were available I had to buy the pair. They don't get the shade you spoke of., when they get bigger I think they are positioned to shade each other. Looks like the loquat in the background will shade them in the afternoon when it matures too.

Thank you too. I figured as much. I'll keep updates posted.

I had two first year trees bloom around the same time. A golden delicious and a donut peach. Five blossoms and two blossoms. Neither apples or peaches formed and fell off as flowers.