I'm sorry to say that the note is absolutely wrong.
Being a web application installable under Tomcat, AACG is installable on every platform that support Tomcat.
As a proof, I've installed it on a 32-bit server with no problem at all.
Simply download the 64-bit version and there you go!
I think this can only be said if you don't care for support. If you want support for the product, according to the note Oracle Support will not support you if you're running the AACG application on 32-bit. If you note the note states that the matrix is a support matrix, thus 64-bit only. If you put it on 32-bit, then you're on your own as Oracle Support will be hands off as the support matrix is strongly enforced from my experience.