Perplexity-User is separate from PerplexityBot. PerplexityBot crawls to build the search index and respects robots.txt; Perplexity-User fetches on behalf of a specific user action and does not.
The practical takeaway: allow PerplexityBot so you are in the index, and do not rely on robots.txt to keep content away from a user who asks Perplexity about your page directly.