He said he was a new member. Perhaps he simply wasn't told yet. Maybe they first wanted to see he's in Akatsuki to stay, or more likely the big boss just hadn't bothered to tell before now. They are villains, after all.

This was a decent enough episode even though Naruto's stupidity was once again underlined too long. I was actually already beginning to doubt they would choose this simple method of allowing him to proceed because even somebody with Naruto's lack of intelligence should have been able to figure that out immediately - after all, he already did in the first place when he ended up using a clone to help form a rasengan. It demonstrates a somewhat unlikely and epic level of idiocy when they make him invent a wheel two times.