Would someone please explain this?

Best is history only, not current. If you beat the best it will change when you update.

 

Best is probably short for "Previous Best" and the Average probably is short for "Average for this segment". There isn't much room on the screen so they shortened it. I agree it is cryptic and confusing. I never bother to look at that screen because it just confuses me.
The 14.1 could be several things. Most likely the car was sitting while the techs were working on it, and the gas engine kicked on and off without going anywhere. Another possibility is that the car was being moved around very short distances while cold, so it never warmed up. Gas consumption can be shockingly high when a car first starts from cold. Much lower consumption once it has run a short distances gradually averages this out.

 

It all depends on which time periods the 2 values are calculated. The user's manual has possibly more information about that.
If the average is "since you bought the car" and best is related to the last x trips since your tank, they will differ, a lot.
If you fuelled up the car and the Best resets, as I think the new Prius does now, and you had only 1-2 very short trips, it might be that the best is reall 14.1, because another one was maybe 9.
I would say the best is to check the user's manual and make a reset of all counters after fuelling up to see how the behavior of the counter really is.
I wish I had my Gen4 to help you more with that.

 

Don't reset all of the trip counters! Each one has it's value. For me, I have "B" as lifetime statistics. "A", I "update" for each tank.

 

The Gen4 has an "ODO" average fuel consumption - to reset it you need to select it and then reset it by pressing Trip for some time. Page 110 of the user manual.
Trip A/B are also still there, and new is the "Mileage since hybrid system was started", which is automatically reset each time the hybrid system goes through a on/off cycle.
So what I meant, is to reset the A and B trips possibly at the next fuel up and see what happens.
I suppose what is shown in the dashboard smaller LCD screens is the same as what shown in the main big LCD in the console...

 

Not sure if this will make sense.

I was screwing around on the big screen and hit the update button just before making a short trip down my street in EV mode.

Over that very short distance my MPG was ridiculously high -- 90 mpg or something like that. Cool-- I wanted to see a big number for my "best" even if I was cheating.

I hit the update button again at the end of my street and the 90 MPG sticks.

Now that is great if I want to show off but I soon come to my senses and realize having contrived number is just stupid.

So I then hit the clear button up top on the big screen and basicaly start over. Or so I think.

So now that I ha returned to my sense, I just hit the reset button when I fill tank. If my MPG for the latest tank is "Best" the new number will be registered. If not, the "Best" remains unchanged.

Prety good.

I kind of screwed up, however. Had I not felt the need to hit that clear button, I could have had my lifetime MPG show up on the same line as my lifetime odometer -- and have that lifetime span also sync up wth the screen that shows EV% and avg speed since day one. Oh well.

 

I "reset" when I fill the tank. Keeps it nice and simple.

 

Ditto, reset both every time since sometimes I will use the other as a data point for specific segments.