Jake arrived in front of a cave.
The lake that was next to the cave was where he just hid a few minutes ago. This was a very good place, and any monster would want to fight for it.
So it made all the more sense that a terrifying monster like the dinosaur that Jake just baited into fighting was the one that occupied this place.
After a whole two days of trial and error, mapping and selection, they chose these two monsters that happened to be right next to each other, and made them duel it out.
So now, with the cave completely free, Jake could just walk in. He calculated for hours to get the timing right. Because even though he was banking on the fact that the dinosaurs in the middle of battle were going to die, there were two that he needed to fear.
The partners of these dinosaurs.
And after observing, they saw that they went out during this time to get the food for the female dinosaurs and presumably for the children.