Termite and Wood Boring Insects - Carpenter ant problem?

Hi, I think this is a false alarm, but please humor me. I moved into an 8-year-old house about 2 months ago. A couple days ago, I was inspecting the ductwork in our finished basement. I opened an access panel in a finished closet and noticed what looked like tunnels in a wood beam. My first thought was carpenter ants, so I did some research. This leads me to think I overreacted.

Reasons I don't think it's ants:
1. The wood beam in question is not moist or water damage at all--it appears very dry.
2. We haven't seen any ants.
3. There is no similar damage to any wood in the furnace room and workshop, and a few other places with exposed beams.
4. The "tunnels" are filled with sawdust. I would think the ants would get rid of that.
5. The "tunnels" are really just on the surface, and don't seem to form galleries.

Now I'm thinking maybe the previous owner who finished the basement used some type of power tool on this wood for some reason? Testing out a router bit? I dunno.

http://i211.photobucket.com/albums/bb279/MGB2/ants.jpg

Mystery! Woodboring insects typically tunnel into wood. And there are usually exit holes. Carpenter ants usually do not have exit holes. They excavate galleries in wood. While most often attracted to wet wood, they can be found in dry wood. The longer they remain in wood, the greater the structural damage.

http://www.extension.umn.edu/distribution/housingandclothing/images/1015f01.jpg

Photo Credit: University of Minnesota Extension Office

Looks like a Roto-zip mark. A roto-zip is a small hi speed router used to cut out drywall, etc.

Looks like a Roto-zip mark. A roto-zip is a small hi speed router used to cut out drywall, etc.

HAAA!!! That makes perfect sense! The guy was cutting the drywall to fit these plastic access panels so that he could access the ductwork. I'm 100% sure that's what it is. Thanks a lot for the answer! :D