NHS notifications

[Herecomethedaffodils]

My son lives with his girlfriend and 4 other housemates and 5 of them have had positive results over the last 3 days. My son had a test today so is awaiting results. I saw my son and his girlfriend on Wednesday evening but I sat in the car and chatted to them for 20 minutes as they stood outside in the rain at the end of the garden path. This morning I have had the notification that suggests I have had possible exposure to COVID, I assume because of my 'close contact' with them as I haven't really been anywhere else. My son has had the same notification 5 times because he lives with these people, which makes sense. But I would have thought that now his housemates have all inputted their positive result into the app, my son should have received a more significant NHS notification telling him to self isolate but he hasn't had one!? Does anyone know why?! Is it just a delay? Obviously he's self isolating anyway as he's in a household with positive cases. None of them have any symptoms.

I know this sounds strange but there is a very good chance that he hasn't actually been within 2 meters of any of them for more than a few seconds (and even if he had he may well have not actually had his phone on him or the blue tooth turned on) so may well not be a contact for the purposes of what the app considers. The app doesn't ask which other app users you live with so can't actually create notifications for those who need to isolate solely because of living with a positive case (and to be honest if people can't tell people they are living with to isolate the country would have bigger problems).