Cheating or luck?
Everyone of us has met someone who played like he would using some chess programe... Lets think about it..
Every chess player has good days and bad days. If I use my own experience, there were many days I have lost to a very low rated player...I lost everything these days.... BUT! There were some amazing days, when I have beaten everyone and my rating jumped up about hundred points...per day.. I could beat even Magnus Carlsen that day (just kidding, of course). This is one of the questions you should thing about.
Many times I was called cheater, but many people don't think it seriously, they ere just angry, disappointed, sad, and maybe they have just bad day and they need to unleash the anger from bad games.
Next reason could be such a small things like that they are warmed up, fresh or they could be in good mood (that could make almost miracle, believe me)
Last thing... Before you mark someone as a cheater, watch your game again, find out what you made wrong and then think, if your opponent really cheated, or if your performance in the game was good or bad. Many times players defeat themselves...
Thank you for reading and have a couple of success. :-)
Play calm, focus your mind, don't cheat and give the best from your hearth.