Regarding:
I have also experienced (and reported) nearly instantaneous kudos from both new and old accounts who were offline at the time.
For what it's worth, there's a setting in a user's Esri Community account that can be used to "show online status to: no one". I've had my account set up that way for several months.
So, I suppose a user could have been online, but when you looked them up, they might have appeared offline. However, I doubt many people know about or use that setting.
Further, some of those settings don't actually work -- I'm not sure if this one works or not. It's currently 8:20 a.m. Eastern time. I'm logged in to my Esri Community account. Do I appear online or offline? (show online status is still set to: no one)