Alex got a little scared. He didn't think he could fight scorpions right now. His body was still suppressed quite a bit by the pressure and his sword was nearly useless.
Fighting any monster right now was difficult for him. Fighting 2 monsters at the same time were completely suicidal. There was only one thing that Alex could do right now, and he did exactly that.
He ran.
He ran away from the scorpions and maneuvered his direction towards the river. However, the pressure in the area was stopping him from showing off his best physical ability, and running in the sand wasn't exactly the easiest thing to do.
As such, his overall speed at running was very weak. The scorpions didn't stand there either. The moment they saw Alex run, they followed him as well.
They were used to the pressure and their exoskeleton was strong enough to handle it right now. And they didn't have a problem running in the sand as Alex did.
