The initial shot showing the front of the hospital shows that it is night but after that when the mob is running up to gather in front it's quite bright on the streets.
Not only would have been impossible for the Mole Men to climb six miles to the Earth's surface without some form of assistance, but the change in atmospheric pressure would have given them the bends.
After Superman escorts the little men back to the well and they go back down he shuts the lid but doesn't bother to latch it.
Superman abandons the uninjured Mole-Man to be hunted by the mob, rather than bringing him with him to safety.