Eric is right, those are very broad questions.
Let me try to put it this way. The Catechism is the teaching of the Church. It contains the Church’s teachings on doctrines - in other words, it tells us various things that are true.
Theology is more a matter of why, how, or in what way those things are true. So for example, the Catechism tells us that Baptism regenerates. Theology would explain how baptism regenerates, and its implications for other aspects of the faith.
Now to a certain degree, the Catechism does contain theology, because first of all, theology is based on doctrines, and so any doctrine the Catechism explains will be the root for some other theological point, and because second of all, some points of doctrine simply are theology. For example, the definition of faith is a theological point.
Now a key difference is that theology can differ in some ways, whereas doctrine cannot. For example, we humans have free will. Now Thomistic theology explains that one way, whereas another school of theology might explain it a different way. The end result is the same, but the explanation for how it works is different. It’s like having a truck that moves, but some people think it’s got a gasoline engine and others think its got a diesel engine. If you know anything about engines, you’ll know that the two are quite different. What everyone looking at the truck would know for certain is that it drives. People might, however, have different opinions as to just how it does that.
So what the Catechism says is true. If someone differs on the catechism, then they are wrong, regardless of what theological idea they are trying to support their belief with. On the other hand, there might be the occasional case where a person seems to be contradicting the Catechism but they in fact are not because they are delving deeper into a given topic than the Catechism does. In general, what the Catechism says is pretty clear, but there are a few times where it doesn’t speak in as gnitty-gritty a way as would be necessary to explain the entire truth. In this occasional case, some person might indeed have an understanding of theology that does get into the gnitty-gritty and doesn’t in fact contradict the catechism.
It’s also possible that they are speaking in theological language that seems to you to contradict the catechism but doesn’t in actuality.
I do think, however, that these particular instances would be rare.
Can you give an example of such a time a friend said this? That would be helpful in explaining to you what I’m trying to say.
Peace and God bless