As someone said above, the kid may have only gotten 1 point off (out of some larger number) due to the methodology. The 15 was NOT Xed out and another answer put in.
Some of my kids had a math curriculum (name escapes me at the moment) that reportedly taught it in a spiral fashion. In the beginning of the year the concept was introduced lightly. It was later revisited in a more complex way. It was sometime hard to help with homework when as a parent you know an easier way to do it, but they haven’t learned that yet.
Our district still teacher algebra in 7th grade to advanced students and algebra 1 is typical in 8th grade for almost all students. Common core has not changed that.