Facebook Message Request question

Not quite sure where to post this but I’ve Googled and can’t find an answer.

I know how message requests work and what send, delivered, and seen mean. I sent a message to someone who isn’t my friend so I know my message went to their message requests.

What I’m confused about is it was on seen for a few days then changed to “delivered”. From what I understand, messages to non friends should only show sent until they’re accepted, then read. This person hasn’t messaged me back either. What’s it mean that I’ve been left on delivered?