In response to Polarbear and Chewbacca: I think that because someone at the testing centre was positive, is why your relatives got pinged, even though there had been no contact. A friend of ours knows someone who works for Test and Trace who says yes, they are sending out pings at random.
I went out for a coffee a few weeks back with an acquaintance, who presented their phone to the black and white dot thingy to register. In conversation I mentioned that they were using it because of working for the NHS? The response was no, they didn't trust it as far as they could throw it, didn't have the app on their phone, and just went through the motions for a quiet life.
Iwas always dubious about the app at the start, and all these examples I think supports my decision not to have the app.