This query came into my mind today whilst sat in traffic on the M62 and my watch vibrating. Any chance they are like mine was today and an health 'reminder' that you've not been active for a certain length of time? Mine suggested getting up and doing a few stretches - would have been quite a sight on the M62!
I was thinking the same, that they could be reminders to "stay active".
Saying this, I was on the M25 for about two hours on Saturday and I did not get any of these notifications. I did find out when I got home that I had climbed 10 flights of stairs, somehow 😄