I have to be very careful here to not say too much. However I will try to give you a birds eye view of how judging works both in real life and the game.
In real life judges are given criteria upon which to judge a round, our judges are given the same criteria. Just like in real life some judges will have a slight bias towards one area of the game than another. This is not intentional in real life but a judge with more experience in BJJ for example might see the nuance to a fighter's technique when grappling which the other judges miss and hence give a higher score in a grapple heavy match. As our judges receive exactly the same data we have given them each a small bias otherwise they would always score identically which would not reflect the reality of the sport. Just like in real life at the end of the round each judge tallies their scores based on what they saw filtered through their own biases and if the difference between the scores is significantly large they award a 10-8 round to the victor.
In the case of a grappling heavy round with limited standup striking and few submission or GnP situations most of the scoring will come from this section of the rules:
"Successful execution of takedowns, submission attempts, reversals and the achievement of advantageous positions that produce immediate or cumulative impact with the potential to contribute to the end of the match, with the IMMEDIATE weighing more heavily than the cumulative impact.” It shall be noted that a successful takedown is not merely a changing of position, but the establishment of an attack from the use of the takedown. Top and bottom position fighters are assessed more on the impactful/effective result of their actions, more so than their position."
https://mmareferee.com/?q=unifiedrules
I hope that answers your question as well as the questions of any of the folks who actually bought the game.