To recap, @thorin (all in Spanish, via pm in order to avoid to get deleted posts) explained me the situation a bit better, we went thru all settings and all is perfect, no double tap to unlock, no smartlock, no Ok Google detection, nothing wrong. It just unlock in his/her pockets and at every swipe provoked by the fabric (Mmm.. Glove mode on?) it change settings, pull down notifications, try to perform calls and so on.
As it doesn't happen to me with both Z3c and the ginormous C5.. The only thing I can think of is a over sensible power on button.
Does anyone knows if there are known issue with power buttons that are too sensible? This is really my last resort before throwing the towel on the issue.
Ideas? Thoughts?