Mistake to let it take off

My P51 has problem of smooth running at high throttle. Initially I thought it is the problem of my cheap ESC (though it has been no prolem in previous 10 flights). After changing to Hobbywing 40A ESC, the BL can run smooth. However, pre flight check with a clamp meter showed 50A (previously 35A). So stupid that I reassure myself that it is ok.
Eventually, power lost mid-flight after 1 min in the sky. Luckily I can still have control and the plane landed safely.
Air-crash investigation revealed the BL is burnt. My hobbywing ESC does not burnt despite the high current surge! Take a closer look revealed a piece of 2x2mm debris inside the bell, with scratch mark on the magnet, and melted copper wire on the stator.

Likely either the copper wire loosen and expose itself to the magnet causing local short circuit. Or some debris got between the stator and the magnet, and plucked the copper wire out.