Is this old basement floor concrete, grout, or something else?
For sure it is a cementious material utilizing portland cement as binding agent. Anything more specific is speculative. If the uneven, raised surface in the background is covered with similar material, this is almost certainly "shotcrete" or "gunite". Pneumatically placed concrete, cement, or mortar. Based on the sandy surface, it was probably a dry mix placement, where dry material and water come out of the gun separately and are essentially "mixed" on impact with the supporting surface. Proper mixing of this method is largely dependent on the applicator's skill.

The other method is wet mix, where pre-mixed material is shot out of the gun. The quality of wet mix placement is more predictable. When done properly over rebar to proper thickness, shotcrete is just as strong as poured in place concrete. Therefore, the technique is still used, often to install tunnel liners and similar roadway works.

P.S. I actually lol'd at you floor of water comment :)