More like a lot of Zoro fans earlier this thread argued Zoro can bypass King's flame on durability, this chapter he states again he can't unless their fire is turned off.
No. Zoro's opinion on his ability to hurt the seraphim with ACOC is unfounded since none of his KOH attacks has landed on King, thus he assumed he can't hurt King.
King however, does fear Zoro's abilities towards the latter end of the fight W/ his flame on and fled. That's what explicitly show hence it's a fair assumption to say that they will hurt him.
Why Zoro doesn't remember that he questioned King's inability to take his attacks before fleeing to the sky? I have no idea. Probably the same illogical reason why he just understood that the Seraphim are based on King's powers.
Overall, Oda has to touch on that Conversation or it was pointless to include.