I am sitting here enjoying this happy story and the thought occurred to me that most of us probably maintain tanks that induce spawning and I'll bet that quite a few of us never even know it is happening or has happened.
I noticed my 3 white cloud minnows acting strangely one day and 2-3 weeks later sure enough a very tiny minnow is sighted. Lots of shrimp in that tank so maybe it is happening all the time and this one got lucky - who knows?
Anyhow, this kind of surprise is a huge reason to have densely planted tanks. We deserve it.