That sounds like a bug, not an intentional game design choice about the game logic, and definitely unrelated to realism vs not realism. Having either of those as goals would lead to "yeah, bullet velocity goes up when you go backwards" being an intentional mechanic.
That you do less damage if you do a certain movement sounds like fun, emergent gameplay? That's not how I understand either of those terms, but of course, every player likes different things.
Surf maps in CS is actually a good example of an engine bug leading to game designers intentionally use it to design new experience, with the keyword being "intentional" since those map makers actually use that bug intentionally. For me that feels very different from engine bugs that don't add any mechanic, and instead just makes the normal game harder.
As an example for overly realistic physics, projectile damage is affected by projectile velocity, which is affected by weapon velocity. IIRC, at some point whether you were able to destroy some target in two shots of a Quasar Cannon or three shots depended on if you were walking backwards while you were firing, or not.