Yes, originally I removed the "human readable" date/time stamps when I ported the ST device handlers to Hubitat device drivers because there was no mobile app for Hubitat. I left the Unix/Epoch-based date/time stamps for people using WebCoRE on their Hubitat, though. That string of numbers is simply the number of milliseconds since Epoch time (00:00:00 Thursday January 1 1970) for when that event took place.
Since then, the Dashboard feature was added, and people who love to see exactly when something has happened on every device starting asking for a custom date/time attribute to be put back in the driver.
However, other people, who hate having their events list cluttered or feel that it may be slowing down things, have asked for a way to disable the custom date/time attribute events altogether.
So, I am going through each of the drivers and adding these features. The one from your screenshot for the Motion Sensor has not yet been updated. I hope to get to it soon.
Thank you for your patience.