As Skizzy tested with Animated armor + Cursed Blade (which is same idea than moonfang + moarg), the animated armor takes precedence IF AND ONLY IF the damage was more than 1 prior to attacking.
With Moarg + Moonfang, if the same interaction is applied, it would mean fireball would hit moonfang for 1, but using shiv/fan on knives/etc (whatever does 1damage as spell) would hit moonfang for 2 damage.
When it happened to me, I think there was spelldamage on board, so it contradicts with cursed blade interaction. Maybe those 2 seemingly same interactions are not coded the same way, but in any case, any “Only” card should take priority, or the wording on the card should be changed.