Series of holes in periphery of basement slab

Hello all,

A quick summary then a couple of questions:

During the heavy March rains and melt in Toronto, my basement floor was wet. Lifting/removing the carpet and underlay revealed a layer of what I think is a thinset mortar improperly laid in an attempt to create a level floor. After a few days of running air movers the thinset has pretty much completely delaminated from the original slab, and can now be peeled away using a flatbar (heck, even my hands). I understand enough to know that without first abrading then applying a bonding agent, any type of concrete product will not adhere to an existing concrete slab.

As I was removing the thinnest, I was surprised (and confused) to find a regular series of ½" diameter holes drilled through the floor. These holes were bored after the the thinset was poured, as I can see that the underlay adhesive was acting as skim over the hole(s). The holes are exactly 8" from the perimeter of the foundation walls, and vary randomly from 12-24" on-center. It's almost like someone snapped chalk lines parallel to the foundation, then walked along with with a hammer drill and a ½" masonry bit. The holes are completely bored through the the slab (wire coat-hanger probes measure a 3-4" slab depth). I can shove the wire further in the soil below. Now that the slab is revealed, I find a decent concrete floor (sloped towards the floor drain (which was hidden under vinyl-roll-type flooring)): This slab was not floated smooth, but has generally decent slope, no cracks (happy surprise), and no signs of spalling or staining.

My Questions:
1-Why would someone drill a series holes through a slab into the ground below? My guess is that a previous owner (we've owned the place for 3 years) must have experienced a flood and drilled the holes as 'indoor weepers'. My problem with this is the regularity with which the holes were drilled - If the water table rises, you're just going to get more water back into the basement. I don't think they would have been for stud-wall anchors (8" offset for a 13-foot wide house would really reduce floor space, and you'd think they would not drill all the way through the slab).

2-Would it be appropriate to fill these holes with hydraulic cement compound? I'm thinking of either a King swift-set or plug-tite product.

Any suggestions as to why the holes are there, and how (or not) to plug them is greatly appreciated. Thank you.