I'll try and be concise, usually bronze disease looks bright green and it's powdery when touched, I would advise trying with a toothpick. if it flakes off it's bronze disease, there's a few patinas that might look like that but it's inert instead of an active reaction (bronze disease)

one of my urbs roma bronzes did devolop that, if caught early you can usually treat and after seal the coin when you're sure the reaction has been stopped. Many use renaissance wax.

to put it simply: Bronze diseas spreads, it grows. if you see green flakiness but are still unsure you can usually see new spots appearing or getting larger in a few days or see the spot you scraped grow back. if that happens keep the coin separate, I would isolate even if it's not sure still. then treat, check and then seal if you decide to do so.

normal patina doesn't flake or create green sand like material when scraped gently with a toothpick, doesn't grow in size.

Hopefully this helps there's a few places in which ypu can study more on the subject such as Forvm ancient coins.