I live in regular fear that my fingertip will hit the wrong up/down icon.
I do it all the time and sometimes I notice and unflag an article. But often not.
I find accidental flags rarer due to the layout versus things I'm trying to tap, however the few times it's happened I only discovered it days or months later when visiting the "flagged" page [0].
Still, there's a kind of guilt, like realizing you unknowingly kicked a puppy who isn't there anymore.