Repairing finish on basement block foundation wall
I think you answered your question when you stated "some type of plaster".  That's exactly what it looks like to me. Plaster is usually applied over lath strips but can be applied straight to concrete but it doesn't last as long and is prone to crack, chip and damage to moisture. It is relatively easy to patch by just mixing more plaster, according to manufacture guidelines, and applying it to the damaged area after thoroughly removing the crumbly old plaster. Check the area for cracks before applying any plaster and repair any seams. There doesn't appear to be a lot of damage so this might be all that's needed.