Yes, this is true, of the following two references I'm not sure which is more accurate, either way this happened:
"Insurgents shot down a U.S. military helicopter during fighting in eastern Afghanistan, killing 30 Americans, most of them belonging to the same elite unit as the Navy SEALs who killed former Al Qaeda leader Usama bin Laden, U.S. officials said Saturday. It was the deadliest single loss for American forces in the decade-old war against the Taliban."
"U.S. officials tell The Associated Press that they believe that none of the Navy SEALs who died in a helicopter crash in Afghanistan had participated in the raid that killed Osama bin Laden, although they were from the same unit that carried out the bin Laden mission."
"The sources thought this was the largest single loss of life ever for SEAL Team Six, known as the Naval Special Warfare Development Group."
The thing about blood, though, is that there's always more to go around.