Pre cum. I don’t get it

Can someone please explain the experience of

Pre ejaculation? (Lol know we are mostly ladies here, but)

My partner and I got lost in the moment and didn’t use protection. He knew I was fertile so he slowed down and came out. There was a definite pause and then he ejaculated. I wasn’t worried because he said he was sure he didn’t orgasm inside, but when I asked if he knew he had pre cum he said he didn’t know.

......

I thought you could tell! how can you not know?! Am I crazy