I can see how that happened
You say it when you see a hot woman with a kid because you're too lazy to ask for her number. It’s like you’re giving her a compliment with a baby.
He said, 'I can see how that happened,' when she walked into the restaurant with the baby. He didn’t even ask for her number.
She was walking with the kid and he said it like he was proud of her.
He saw her with the baby and said it like it was a personal achievement.