You’re right, but it depends on how you want to think about it. They’re not necessarily graded on a curve, but with standardized tests you usually have both a history and a design target. They’re intended to produce (for example) a normal curve with a specific mean (eg mean IQ = 100) and they’ll adjust the test year over year to keep within those bounds. In other words, the grades don’t change but the test does.

Curves exist because failing 90% of your class is a really bad look.