Trust This Computer?

Watch (series 6 WatchOS 7.5) has been in use with the same iPhone and Mac for months. Today, and on at least one other occasion, the trust alert has prompted me for a response. On each occasion the option to trust was taken. What added to the confusion was that the alert wasn’t displayed when I was sat next to all of the connected hardware, but appeared when visiting the adjacent building wearing only the watch (ie the iPhone and Mac and the network for that matter are physically located in the building I had just left).

The documentation clearly states, “These computers remain trusted unless you change which computers you trust or erase your device.” https://support.apple.com/en-us/HT202778

As I would have absolutely no need to change which computers I trust and have not made any significant changes bar the application of regular updates -the last of which will have been ios 14.6 and macOS Big Sur 11.4, the question begs as to why should this alert be displayed especially given the advice in the official documentation?