Forum:Mystical Space Typhoon Vs Monster Equip

Well... Sorry if i wrong, but i got a little question about Mystical Space Typhoon. The think is that the card say "Target 1 Spell/Trap Card on the field; destroy that target" but when i fighted versus one using a dragunity deck, he used mystical space typhoon to destroy 1 monster equiped to a monster he have to activate the effect.

Here is the question ¿Is that Valid? because mystical say "Spell/Trap" no say Monster