It's not plagiarism, you're right. It's your AU and you can do it.
But you said, "I based the canon on the ORIGINAL SPRUNKI." In NyankoBfLol's Original Sprunki, there's no Wenda x Gray canon either. Wenda and Gray don't even interact in the original.
In Misfit Mix, which is the canon that Xeno actually wrote for those designs, it says Partner || N/A + best friend Gray.
I don't have to shut up for pointing out the official fact. Your AU ≠ canon. My comment ≠ hate. End of story.