I thought they were on R&R and were just going to/coming from a place where they could drink some beers....
That's right.
Apparently they had just completed some sort of operation, although not necessarily a combat operation, and some of Cleland's buddies were staying behind for some refreshment. Cleland had already boarded the helo, but changed his mind and decided to stay.
After jumping a few feet to the ground, and leaving the immediate landing area, he turned back and noticed a grenade lying on the ground. thinking it had fallen from his webgear, he reached to pick it up and it exploded.
Obviously he didn't get his beer break that day.
Not on R&R, though. That part is wrong.