In my opinion it's not that impressive either way. If he did remember it: Seems like it's very common for artists to take mental or physical notes of interesti

In my opinion it's not that impressive either way. If he did remember it: Seems like it's very common for artists to take mental or physical notes of interesting things they see. He saw the name, associated it with the cemetery, then forgot that it was a real name and place. If it's a coincidence: Tons of people are buried at churches, that's not unusual. There's a chance there's more than one Eleanor Rigby buried at a church.