Are you familiar with the acronym, "CYA", as in Cover Your A##? It looks to me like that's what the installer is doing, here.
Quick test: get some muriatic acid or sodium bisulfate (pH Down). Mix up a cup of 1/3 acid + 2/3 water. Pour it on the step.
If it fizzes, it's calcium carbonate. Rinse it off after 5 minutes. If there's no change, and no fizzing, take good photos, and check your pool warranty details.
Good luck!
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