Can you put in batteries backward?

I was watching a clip on Acebeam K65 light. This guy showed the battery pack with all in same direction. I have this light and the bat pack is two up and two down for 16+ volts (in series).

What did I see wrong?

I have the X80 (with same kind of batteries and holder), and you're right, the batteries alternate polarity. The only thing I can think of - is that Mat quickly installed the batteries for illustration purposes - only.