I do caps for schraders and capless for presta. My theory is that the prestas don't recess so I can clean them if dirty. Not so for schraders so I cap 'em therefore it isn't that.

I took a closer looks at it and it looks like a cat has been gnawing at it. I sometimes have cats here. Maybe magic cat saliva? Or just a magic tube - one of the formerly leaking ones is from 11-12 years ago from my first ever bike and it still going strong.

My original theory as to the flat, when I found it, was that I left a maxed pumped tire (I do 75 PSI, since it is for commuting, in a 70 PSI max tire/tube) in the trunk of my car which got hot and it went kaboom, but that doesn't make sense at all since a bust like that would cause a big rip and it wasn't that hot.

Eh, maybe I shouldn't complain since it is a good thing. Haven't had to throw away a mtb schrader tube ever.

I need to make a video of this the next time because everyone I have talked to says I am lying and no one is ever around when it happens.....well, no ones that knows bike stuff... - just don't ask me to rub your schrader tubes...