It could be. It could also just be that the engineers had to rush to meet a deadline. Last year during the initial Pixel 10 release the pixels were using a bunch of out-of-tree patches until QPR1 (which also didn't have its source code released until December) because the initial launch was timed right with Android 16. That meant that Pixel 10s couldn't boot anything other than the stock Pixel ROM because no one else had those patches. GrapheneOS couldn't support them until that release in December happened. This could end up being something similar.