Sam
It is very common to have things that al pi halacha is mutar but al pi nistar it should be avoided. I dont think that nistar is saying assur just saying strongly that one should avoid it. Thats not a stira. A stira would be if shulchon aruch says flat out that a non Jew may be in the succah and nistar says no he may not be. However in our case halacha didnt say one way or the other so taking on the nistar aspect is recommended when possible.
I just want to clarify that I am not racist or bigoted in any way and I make sure to treat non Jews with respect as human beings however I do recognize that “ata vechartanu mikal hoamim, ahavta osanu veratzisa vonu veromamtanu mikol halshonos vekidashtonu…”