Appears to be more something along these lines.
Expansion joints permit volume change movement of a concrete structure or member. These are usually constructed by installing pre-formed, or pre-molded elastic/resilient material of approximately 1/4" to 1/2" thickness as wide as the concrete is thick, before the concrete is placed. Expansion joints should never be less than 1/4" wide. Pre-molded expansion joints for installation in residential, commercial, or industrial slabs may be of fiber, sponge rubber, plastic, or cork composition. Such materials must be highly resilient, and non-extruding in hot weather, or brittle in cold weather.
An expansion joint should always be utilized where a concrete member will join or abut an existing structure of any type. This would include a junction of sidewalks, sidewalk with a driveway, building, curb, or other similar members, as well as where a floor slab joins a column, staircase, etc. The square formed by the intersection of two sidewalks should have pre-molded expansion material enclosing the perimeter. Normally, expansion joints are not provided in sidewalks other than where the walk abuts an existing structure.
Expansion joints should also be provided in a building floor slab where the slab abuts walls or footings. Sealing of expansion joints is desirable in many outdoor or industrial/commercial applications.
What do control joints or “expansion joints” look like?
http://www.inspect-ny.com/structure/Concrete_Control_Joint062-DFss.JPG The photograph at page top and the photo just above where Andy is walking away from the camera show expansion joints in a garage floor slab in Arizona. Even in a climate where we do not anticipate freezing, control joints are needed to prevent random shrinkage cracks that would otherwise occur in a large concrete floor slab pour like this one. Notice that we do not see other cracks in this slab. Control joints are likely to appear as straight lines at regular intervals across a poured concrete slab (if they were used in the construction of the slab) such as we show in the sketch below, at the lines marked (G) at 4’ intervals or larger depending on the concrete materials and slab design used.
http://www.inspect-ny.com/structure/Concrete_Control_Joint060-DFss.JPG http://www.inspect-ny.com/structure/SlabCracks046DJFss.jpg Shrinkage cracks that occur at control joints such as shown in the pair of close up concrete slab control joint crack photos here, are occurring where they are supposed-to. The fine crack shown in the left-hand photo of a concrete slab control joint is normal - this crack would have occurred in a random pattern instead of along the control joint if this floor slab (the same floor shown at the top of this page) had been poured without any control joints. In a different building, the width of the control joint crack in the right-hand photo above was surprisingly large. These cracks are not normally a defect in the slab but may be a source of water or radon gas entry into the building and may need to be sealed.
Quite possible that it is somewhere down these lines.
Concrete floor contractor in the area would be recommended to find the actuall reason.
Different methods and products for different geographical areas.
Hope this helps a little.