The truth is, it cold just be a scab from a scratch. That happens to Monte several times. Scratched by himself or by another. The most important things are: Is it inflammed? is it oozing? is it painful to the cat when you touch it? Does it look scaly, like it is dry as well as scabbed? Answeres to these questions will help to narrow down the cause of the scab.
P.S. Your cats are adorable! looking forward to seeing more of them.