The time displayed in the short summary is not the time of the last activity post, but rather the last time that the member was active. This means if that member logs in, the time will reset and display “A few second ago”. This is the default BuddyPress behavior so unfortunately we can’t change that.
Of course if you believe this is a bug, you can always contact BuddyPress support to see if they can help:
You're trying to setup your theme but you're experiencing errors when importing the demo content? Or you've just followed the setup guide but your website doesn't look exactly like our demo? These are common issues for which you can find easy and quick fixes.