Streamers who respond to their viewers on streams or VAs who chat with a fan at a con or answer asks on social media are interacting in a professional capacity, not a social one. I'll give you BNFdom being blurry, but that's still not the same thing as someone you're deliberately interacting with one-on-one as part of a social hobby.

There is nothing remotely parasocial about your relationship with someone you chat or thread with. At all. Assuming they aren't just one of the many, many people who uses "friend" as shorthand for "friendly acquaintance", it's possible for them to be overinvested, but it's still an actual social relationship. It's up to you to make your boundaries clear, and disengage if they push them.