That's real. Asians show a massive (compared to anything else that moved) NAEP score increase over the 25-year period, which is presumably tied to changing English-language competency as a group. It matters less for the overall average score as their population share is much smaller.
If you want more data on something or other, you should state the hypothesis that you are trying to test. Mine is pretty simple and was easy to test like I did in the first post: in a world of mostly static in-group NAEP 8th-grade reading scores (like the one we live in) large shifts in population shares (like we see) dominate the overall average.