It had to be known that Atlas wasn't fighting in an isolated environment. He encountered only a few people at the beginning, but as he progressed further, he found himself surrounded by more and more scenes of battle.
His current fight was taking place in a corridor where a few other people were also fighting, but for the most part, everyone ignored each other and stayed in their own lanes. At most, they kept their eyes on each other so they wouldn't get stabbed in the back.
The number of people was what made it easier for Atlas to utilize invisibility and approach them without being noticed. More importantly, it served as a perfect mechanism to aid him in his escape.
The further he went into the tomb, the more crowded the area would become. Most people were already each other's enemies, so he, as someone who blended into the crowd, would be able to progress at a relatively smooth pace.
