To the OP----I have had it happen where the wire embeds itself into the tread and even riskily running my thumbs along the inside of the tire (great way to get nasty cuts) won't show a wire .... but when you hit a bump just right the wire will protrude into the tube ... sometimes giving such a small puncture that it is impossible to find without a bucket of water and really high air pressure ..... but still somehow enough to drain the tire to unsafe levels after a few miles of riding. (Someone needs to teach these tube Physics.)
I always bring two tubes and usually temporary patches .... and even so sometimes everything fails repeatedly. Welcome to Life---it doesn't always suck.