Not sure what you're question is...
If it's "How did this happen?", then it was probably an errant mouse click. I do this once in a while too, just keep an eye on the statistics panel now and again.
If it's "How do I get rid of this?", then go into modeler, use the statistics panel and select all skelegons, hide the unselected geometry of the model. Deselect all skelegons then use the statistics panel again to select only the one-point skelegon and delete it.
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