Worshiping?

Could be all of them reacting to the event that wiped them out. The one is bracing for impact, the one behind him is shielding himself from said event behind his fellow engineer. The one on his knees has his arms up and is bracing for impact as well, shielding his eyes.

Looks to me as normal reaction (for humans anyway) to some horrific event; Microwave blast, Electro-Magnetic Pulse, loss of cell phone signal, radiation-resistant genital crabs...that kind of thing...

They may be worshipping outside temple shown along with the crowd seen scorched. 

What if, the smaller figure is human.

The Engineers abduct humans from pre-historic Earth to use as guinea pigs in their science experiments?