A little research shows why he might have been a target, though. It appears that "Seh Daeng" (real name: Khattiya Sawasdipol), however, has a long history of refusing orders from the government and was even stripped of his rank and has even met with ousted Prime Minister Thaksin, who is wanted on (possibly trumped-up) corruption charges. He has also been accused of leading a group of armed men who attacked other soldiers last month.
So far, the protesters are standing firm, but there are also reports of explosions in Bangkok. This situation looks to get far worse before it gets better.
This is a big issue for the US because Thailand has long been our strongest ally in the region, and it already has one insurgency in the far south. If Thailand collapses entirely, it will set back US interests in the region dramatically. We have relationships with other ASEAN members, but the only other ASEAN major ally is the Philippines, which also has an ongoing insurgency and cannot help us with issues on the peninsula. My fingers are crossed that this finally blows over, but it is looking ugly now.