Sam2,
I am not 100% sure what you are referring to. Are you talking about the Shulchan Aruch about not walking 4 amos with an uncovered head or the Shulchan Aruch about not looking at the makom hatoref?
The Shulchan Aruch didn’t just make these statements up out of nowhere. For example, the Shulchan Aruch’s statement that it is assur to look at the makom hatoref is based on the shitah of Reish Lakish in Nedarim 20a, and is meduyak in the Gemara in Berachos (“????? ????? ????? ?????” implies that there is a separate level of issur for the makom hatoref).
It is not a leap to think that Rashi would read the Gemara in Berachos to be consistent with the Gemara in Nedarim.