I'm not saying anything in spite of the rulings.
Look at the 2 pieces of text, 1 on the card, and that 1 ruling again:
Horus the Black Flame Dragon LV8
Effect Monster (Dragon / FIRE / 8 Stars / ATK 3000 / DEF 1800)
This card cannot be Normal Summoned or Set. This card cannot be Special Summmoned except by the effect of "Horus the Black Flame Dragon LV6". As long as this card remains face-up on your side of the field, you can negate the activation and effect of any Spell Cards and destroy them.
The text on the card allows Horus LV8 to negate the activation of any spell card. Field, Continuous, Quickplay, Normal, and Equip.
Now, to shed a little light on ruling you brought up:
"¢ You can chain the effect of "Horus the Black Flame Dragon LV8" to the activation of a Continuous Spell Card, Field Spell Card, or Equip Spell Card and negate it. However, if the Continuous, Field, or Equip Spell Card is already active, you cannot later decide to try and negate its effect with "Horus the Black Flame Dragon LV8". You can only negate it when it is originally activated.
This ruling is making a distinction between activating a NEW Continuous/Field/Equip Spell Card vs. One that was already activated and currently active on the field when Horus LV8 is Special Summoned to the field. What they are saying is that Horus LV8 CAN negating the activation of any of those kinds of spells. However, since those types of Spell Cards have "Continuous" effects, Horus LV8 can NOT negate a Continuous/Field/Equip Spell if it was already active prior.
Normal and Quickplay Spell Cards aren't mentioned since they are only on the field for Activation/Resolution (except for Spell Cards like, "Swords of Revealing Light" and "Different Dimension Capsule". Even though they are Normal Spell cards, their effect keeps them on the field for more than the current turn. However, they would fall under the same rules as Continuous Spell cards since they could already be Active prior to Horus LV8 hitting the field).
Hope that helps clear it up.
- A