What's the problem? This is a huge problem!!
Duncan stared at the old man before him, and quickly realized that Maurice did not understand what the jetting flame stream he saw meant—this scholar did not know about the Sun Shard, and he very likely mistook Nina for another "Transcendent being," such as Duncan's own follower, or something else that had escaped from Subspace.
Indeed, that's what Maurice thought. The moment he saw the jetting flame stream, he regarded his "student" as a being similar to Duncan. As to why this "Subspace family" looked like a giant in one instance and like a flame in another, he didn't think too deeply about it—Subspace oddities were the norm, after all, and that place wasn't known to have any living people; the big shots could look however they wanted...
However, now that he saw Duncan's reaction, Maurice finally started to vaguely realize that the situation might be different from what he had guessed.