Have you been in London recently? I think the safety check algorithm must look at your location history for the last n days and ask you if you've recently been in the area.
I live in Manchester, but was in Bali when the bomb went off last month. I got the safety check. This made sense as my friends might not have been aware that I was away, and so it was useful for them to be alerted that I was safe.
I live in Manchester, but was in Bali when the bomb went off last month. I got the safety check. This made sense as my friends might not have been aware that I was away, and so it was useful for them to be alerted that I was safe.