So, let me get this straight. Joseph notices that Mary is pregnant. Joseph confronts Mary about it. And Mary replies: err, hmm, I know, the angel of the Lord came down and impregnated me. We’re going to have the child of God. And Joseph is like: okay, cool.
It’s a rehashed, remade, repeated story.
A lot like how we all all repeat and repost memes on social media.
Someone came up with the original story a long, long, long time ago and it got reposted. Then the Egyptians told the same story, then the Greeks, then the Persians, then several other middle eastern tribes (I don’t know the details but it was a repeated story) … girl gets mysteriously pregnant, claims god dropped his seed and now she’s carrying the baby.
No one knows who the original OP was … probably some hunter gatherer that left his girl for a month and came home to find her pregnant and now had to come up with a story to explain it to people. Then his original post just got repeated a thousand times.