20 years in pest control here.
Get the game inspected/treated now.

If the colony is mature they can swarm into your home.

Call me when that happens. It's big money and an easy sale for me.

you can also drill into the wood, inject a termiticide foam into the galleries and kill the termites.

this could be an option for you.

You will want to drill a small hole in the areas where you see the exit holes. This is where the gallery is. Pm me for greater details.
I can walk you through this.

you are 1/3 correct. subterranean termites live in the soil and build mud tubes and attach to wood. dry wood termites do not need earth to wood contact and are often found in attics and window sills. damp wood termites are rarely found in homes but are mostly found in wood near bodies of water like swamps.
putting wood on a concrete slab is not a guarantee that subterranean termites will not infest. I have seen/treated many concrete slab structures that have had subterranean termites come up through cracks in the slab as well as expansion joints. plumbing lines, electrical conduits etc. again, 20 years in the pest control business, a degree in entomology. there are also Formosan termites. they are a type of subterranean termite but where a standard sub colony will number in the 100,000+ range the Formosan colony will number in the 1,000,000"S. the damage they can do in just months is insane.
it should also be noted that termites do more damage to homes and businesses in the us every year than all the fires and natural disasters combined. an estimated 2 billion + a year.

Some pics of receint termite work.

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image_1.jpg

The 1st pic is under the floor of an apt. Building. Notice the tubes going from the dirt all the way up the concrete pier block. Up the pier post. To the flooring and into the floor joist.
The second pic is of a window sill at an industrial park. This building is on a concrete slab. The many bodies are of sub termite swarmers. They are reproductive members. The swarm, fly a short distance. Land, their wings fall off. They burrow into soil and start forming new colonies.

Also known as the American cockroach. Ants have been known to attack termite colonies and eat the termites. This is why termite colonies have 3 casts.
Workers, solders,and reproductive's.

The solder cast is responsible for defending the colony from attack by other pests.

That will work. I did not suggest it only because not everyone has access to a freezer that big.

Some years ago, I had a case where the home owner had traveled to Thailand. He had picked up several wood carved statues and placed them on the mantle of his home. After a couple of months he noticed frass and small holes in his mantle.
I inspected the site and the statues and found them to contain wood boring beetles.
He had a freezer in his garage so he put them in the freezer for 30 days to kill the beetles.
I drilled into the mantle and injected a foam into the galleries to kill any beetles. Filled to holes, sanded,painted,and boom! Good as new.