the heck you talking about? sage world have no matching, you get whoever you click on(or whoever clicks on you)
Guestimating who is whom based on various factors is a huge part of it.

Well yes, but generally there are both high level and low level on every field (unless there are 2 or less of either). So unless you have evidence that one side have significantly more low level, I repeat: what the heck are you talking about?

Your point being? so what if he fought half a dozen relatively low level opponent out of over 40? That distribution isn't exactly unimaginable.
The top level player on my server is 82, which thanks to missions isn't far from 83. If we say 60% of the top 100 player joins, distributed evenly, then we'd have 20 on each side, which is more or less what the video had(granted, our higher level player might be fewer because our server is less active).
We have only about 60 75+, which means that 40% of the entries will be below 75, or 24 of them, roughly 8 on each side. So it's not unthinkable that he happens to encounter a number of them. And part of sage strategy is guessing who are weak (or, in some cases, hunt specifically by the right hand side tool bar) to build your own streak (you c*so hunt down streakers, who are the strongest, but that's difficult as they might be in battle, but let's not get side tracked) so if he is good at what he does, he might just be able to fight more low levels.

The ONLY way to prove your theory is to:
take screenshot of the members of each team BEFORE battle start.
take screenshot of the ranking board AFTER the fight, and color code them according to side. (you might have to append to the end those who sign up but do not join, as those are considered in distributing sides but might not be on the ranking, I'm not sure)
resort the ranking board based on level.
See if the colors are evenly distributed from top to bottom.

Have fun doing that. The stuff you gave proves nothing.

You are trying to assert that there is a bug, I gave you a way to provide conclusive evidence of whether there is one. (oh, and I forgot, also do a sorting based on power, not sure which the game might use, level or power)
If you can't conclusively prove there is a bug, then there is probably no bug.