The two phrases mean the same thing for the most part. I wouldn't use both of them in the same sentence. "I am by no means a techie": The person wants to stress/emphasize that he doesn't know a lot about the technical topic (say, computers). It's like a reminder to the listener. "by any stretch" is a part of "by any stretch of the imagination". So..."no matter how much you stretch the meaning of "techie," I'm not one." Both are saying: Really, I am NOT a techie.

It can mean that this person is not an expert in technology/computers.