That's a really good reason to patch tubes. That and line up your tire label with (or opposite) the valve stem. Then if a hidden piece of glass causes a 2nd flat, it will be in nearly the same place and you know you have to find the culprit or get another tire and you know where to look. I've pulled out many pieces of fine wire about 2 mm long, some that lie entirely within the tread and casing with nothing showing. I'd never find them without 1) knowing it was there and would cause another and 2) knowing the location to within an inch.

Edit: so that wire is from steel belted auto tires? I've been wondering for years because it is a new phenomenon. I never saw it in until the '90s. My big mileage years were the '70s and I was riding tubulars and cheap. Those pieces of wire never crossed my eyes.

Ben