Guild Wars 2

Why is this skill considered projectile ? (it is blocked by Wall of reflection /smoke screen/etc ). on Skill descritpion i see is bombs /blast /explosion (Fire a cluster bomb at target area. Detonate in midair for multiple explosions //Blast finisher)

Lobbing skills are still blocked by walls, but the aoe dmg can hit through them if you shoot the ground in front of the wall~ works this way for many similar enemy skills as well, like the spider boss in Twilight Arbor, the Tree in swamp fractal and so on. (I use Smoke Screen a lot)

because your still firing an arrow with a bomb attached

More like an advanced anti-gravitational explosive device.

No other thing could move as slowly as clusterbomb on earth-like gravity defying all physics laws, so it clearly stinks of Asuran technology.

This is projectile.
This can be reflected back too if arrow hits directly to the reflection source