It is very ambiguous. Atlas says to Dylan "First rule of magic, always be the smartest guy in the room". Dylan tells him he was in agreement, which could strictly mean that he agreed with the statement that this was the first rule of magic.
Anything else we infer has to come from our analysis of their body language and non-verbal cues, which can be subjective. My analysis was that Dylan agreed with Atlas that Atlas was the smartest guy in the room, since he was the one performing magic. Having more information than Atlas doesn't strictly make Dylan smarter, and he may not have thought so. Even if he did, it seemed like he was telling Atlas he agreed with Atlas' implied comment that he (Atlas) was the smartest guy in the room.
Or maybe they added the line because it sounded smart, and didn't really think it through.