I don’t believe angels can read our thoughts. However, because of their higher nature in relation to us, they are able to deduce and have fairly high accuracy when it comes to knowing what we’re thinking. The same would go for demons obviously.
Angels are not supremely intelligent; however, they due have the ability to see outcomes of events and know things without seeing the complete picture. At least that’s what Joan Carol Cruz’s book mentioned. It’s very interesting how a pure spirit can obtain knowledge. How they do specifically is unclear though. However, it does differ from our methods.