Ground level beneath render

[Bex]

Hi hoping for some reassurance

I had rendering done on a large gable end and am happy with result - but they have used concrete to fill the gap below the render to ground level. This is because the exposed brick work was in a terrible state. Can anyone reassure me that this concrete is suitable? My questions are if there is a better alternative ? They are due to come back to do other work so could raise this with them when they return.