You are correct, that s' is a pronoun. However it is a special type of pronoun. A reflexive pronoun. : me, te, se, nous, vous, and se
And the rule for qui/que appears to not be affected by the reflexive pronoun. So the simpler to understand rule here I consider still stands
While for the direct pronouns of : je, tu, il, elle, on, nous, vous, ils, elles - they are accounted for.
So while you are correct that s' is a pronoun, as it is a reflexive pronoun for the rules for qui / que - it does not take affect.
edited: also this is how Duolingo teaches it, though that does not make it correct ;P :
How do you know if you should use qui or que?
A helpful tip is that qui is followed by a verb² , while que isn't!
So thank you for pointing this out.
And I can support your idea to stick with subject vs object instead - however for many of us that is very hard to understand.
I consider it is okay that people find different rules that are easier for them to understand and use. It is okay if we explain things in different ways.
Would you like to explain about subject vs object my friend ?
I have read and listened to some resources - and for all of them - they just scramble my head and I can reliably apply them to assist in determining which to use.
Perhaps you may be better at explaining it, or recommend some resources you find useful.
For there will we others that will find the explanation of subject vs object better for their learning.
edited - I will also clearly add this exception to the top explanation. Again, thanks for pointing this out. Your review and input is greatly appreciated by MANY !! Including me.