"x" is more intelligent than "y" turns out to be a very difficult assessment to make. In humans IQ tests turn out to be almost useless for measuring intelligence. In animals standard "intelligence" tests like the ability to identify themselves in a mirror are starting to crack, eg dog's can't do this but that may be more related to their use of smell more then sight in identifying individuals. It turns out when you perform similar tests with smell they do identify their own smell indicating they do have a sense of "self".
In many cases it all comes down to the test you use and I expect dragons would not score highly in the tests that rank border collies as the most intelligent dog, as these center around how quickly they can learn and follow new instructions. The problem here is what if the animal understands perfectly well what you are telling it to do and just isn't inclined to do it? I imagine dragons would fall into the category of animals that are not particularly inclined to do what they are told, and therefor would not do well in tests related to learning instructions
Are dragons as intelligent as dogs? It would probably depend on the test, but I lean towards no. While they are large and therefor potential have a large cerebral cortex dragons do not really fit the profile of intelligent animals. They do not see like animals suited for large social groups now do they require a lot of intelligence to find a meal. Dogs, on the other hand may be even more intelligent than we realize. For example many facial expressions have been identified in dogs, but it turns out that when there are no people around they only use a few of them. IOW these expressions are not "natural" or subconscious behaviors, rather, it appears they use them as a form of language to communicate with humans.
Ultimately though, this is fantasy so dragons are exactly as smart as GRRM decides they are. As to what he's decided, I'm not sure we really know. That some maesters believe them to be very intelligent doesn't mean they are. They may simply be unreliable or perhaps are basing their opinions on work written to butter up Targaryans or Valyria.
Anyway. Overall I didn't like the scene, it seemed to contrived based on the level of reasoning wev'e actually seen from the dragons even if they were really supposed to be capable of it all along.