You could meet someone 10 times and not recognize them. Pain.
You remembered fewer than half the faces. Your brain looked at those faces and said "they all look the same to me" and honestly it wasn't being rude — it genuinely couldn't tell. You're the person who walks past friends without recognizing them, needs context clues (like someone's outfit or voice) to figure out who they are, and has definitely pretended to recognize someone you absolutely did not recognize. It's fine. Just use the "heyyyy" strategy forever.
Get your read — free on iPhoneyou've definitely introduced yourself to the same person twice and they definitely noticed.