Forum:Stardust dragon, Horus LV8, and cards from the hand

i was in a duel the other day, i have a horus level 8 on my side of the field, opponent has a stardust dragon, it's his turn, and he activates Monster Reborn.

i activate horus' effect, which reads: You can negate the activation and effect of any Spell Cards and destroy them.

can my opponent use stardust's effect? since i am negating the activation of monster reborn, does the card count as being "on the field"?