Meeting for the first time is likely to be your scene at that time or something special about him, which will make your potential memory deep. The human brain is like a super-advanced computer, which never stops. It records what happens around you and your own thoughts all the time. However, when you choose to recall afterwards, your brain will transmit the pictures you have experienced to you according to your potential key tendency principle, and so will dreams.
Occasionally, I think that you may have seen or been exposed to something familiar. You may not have noticed it yourself, but your brain can accurately analyze it, so you may choose to present this scene to you at night.