Yup, it's not sideloading. Actual sideloading would be too much freedom for an iphone ecosystem.
Apple despises user freedom. Their whole thing is "use what we gave you and be happy for it". They would never tolerate letting users do something like run any app of their own choosing.
It uses the word "sideloading" and doesn't appear to have carveouts allowing Apple to block apps for "security" like the EU legislation does. But at the end of the day it really just depends on what their legislators are going to allow Apple to get away with, and Apple will probably attempt bare-minimum compliance at least initially, like they did in the EU.