I replayed the game and discussed it with my opponent. I thought Tortollan Primalist would be a clever way to cast both the 7 and 8 mana cards with a lucky roll. However, only the spell discovered counts. Tortollan Primalist itself does not trigger as an 8 mana card. I'll be reporting this to Blizzard.
Well, I started playing the deck in practice mode and now it's working as designed. The time it didn't work I selected Psychic Scream. Perhaps the fact that the card was no longer in play upon resolution had some sort of effect? It's going to be hard to recreate this scenario.