There is an underlying implication that if some form of angling isn't considered "fly fishing" that it is somehow "substandard" or of less value. I don't believe that to be the case, nor apparently does the OP (based upon their first sentence). So does it really matter if any form of angling is or isn't called "fly fishing"? If suddenly, all the "upstream and dry" purists were no longer considered "fly fishing", would anything of consequence change? It all seems pretty inconsequential to me.
But to play along and "further" the discussion...
For me, what defines "fly fishing" and differentiates it from other forms of angling is the process used to present the hook to a fish. Not whether that hook is a "fly" of feathers, a metal lure, or a worm on a hook.
How do I get there? Let me elaborate.
In most other forms of angling (thank you for using/defining that term Lotech), weight is added to a line with insufficient mass to be effectively cast alone. That weight (a lure, bobber, sinker, etc.) is then cast by the angler, and it in turn carries the "weightless" line with it. (Like in spin-casting) In "fly fishing" the opposite is true. A line already having "sufficient" mass to effectively be cast alone is cast, and that line in turn carries the "weightless" hook with it. Another way to look at it is this: When you cast, what leads the way? If it is the line, then the line is being cast. If it is what ever is attached to the line, then it is the "weight" that is being cast. Line being cast = Fly Fishing. Added weight being cast = some other form of angling.
Based upon my definition of "fly fishing", I'll let you decide if I consider Czech nymphing and/or Tenkara "fly fishing". But I really don't care what you call it. It's all angling, and it's all fun.
---David