The example photo is somewhat misleading, as it actually looks like the same height here.
Nevertheless: If the height difference was commissioned in the construction planning, then this is clearly not a defect, but execution according to the order. There are always things that the client does not like afterwards. Ultimately, however, the fact is that a craftsman can only implement what has been commissioned. Whether it is nice or sensible is initially irrelevant, as long as no serious problems arise from it. However, I do not see that here at first.
What does make me suspicious, though, is: Why unnecessarily make 2 different heights? Even if you want to save those few cubic meters of concrete, you simply make the excavation pit in two stages. The costs for this are negligible and for that you have a uniform appearance, especially no steps and also continuous walls and ceilings. Even as a layperson, I do think about such things in advance. If you buy an SUV, you also can’t blame the seller later for not telling you that parking spaces are tight and insurance is expensive.