I know they've done that deliberately, that's why it sticks out like a sore thumb.

Did you look at the close-up of where the old stonework meets the new brickwork? The stonework isn't pointed properly and before long, it'll be crumbling. I've seen better pointing on buildings they're maintaining as a ruin.

Can you imagine repairing/restoring a vintage car with new bits totally different to the original and also a different texture and colour?