Did they not bother to talk to any flint knappers that use their tools? Flint does great on small game. Not just birds, but birds in particular can be a bit delicate to work on, and smaller tools work well. Imo, flint or obsidian are better than steel for birds, and squirrels.
I mean, I get that it's a hands on, documentation thing, but people still use stone tools, even if it's only for the hell of it.