Keamy appeared visibly upset as he was holding Alex hostage. He appeared to be fighting back tears. He was upset and frightened because Ben seemed to know all about him, evidenced by his anger toward Captain Gault, whom he thought "gave him up."
While he did appear to be experiencing some emotions, I think "appeared to be fighting back tears" and "upset and frightened" are reading too much into mere facial expressions.
Keamy kicked a hand grenade towards his partner Omar during a fight with the others. It is possible that this was a deliberate act because he feared that if captured, Omar would give away information under interogation.
Very unlikely, Keamy probably wouldn't have had time to think about where he kicked it, but just tried to get it as far away from himself as possible before it exploded