I think this is a gifted trait. My DS16 does something similar. He won't answer the question "what is your favorite" or other vague prompts that expect you to make a random choice. For years he couldn't answer it.. period. He would freeze and not answer or not write anything. Teachers LOVE to use this as a prompt for writing and he often just freezes and can't write anything. It's taken YEARS to get him to not take the question literally. It's especially bad when it's something he really doesn't care about like "what is your favorite sport".
Over & over I've explained and had other teachers and professionals explain that it is a prompt to get him to say something. The teacher really couldn't care less if it's really his favorite he just needs to find something social acceptable to respond, or if it's a writing assignment that it's a subject he is comfortable writing about. If it's a person trying for an ice-breaker it's perfectly OK to say you don't have a favorite.
