I'm no expert, but mottling is typically more widespread vs. in small isoltated areas. Not that mottling can't occur in smaller patches...its just that it would be less likely that it would occur in a relatively small proportion of the total surface area.
Some might weigh in with an opinion that this appears to be more related to poor application/troweling technique on your steps, excess calcium chloride in the mixture, over use of water during finish troweling, or curing issue. But I suspect your PB will attribute this to mottling, which is a standard disclaimer in pool finishing contracts.
With this appearing on the steps, it would not require much to drain the pool to expose just the steps, so maybe your PB can acid wash the area again to eliminate or dimish those areas. Others here might have a different take.
Can understand your concern about the look though. Definitely reach out to your PB about these spots.