Try to relax. I've seen quite a few people posting here who got the same "decision will be mailed..." thing, but got their OLs after the normal period of time.
Probably it had to be approved by a senior IO? any idea if your IO was junior/senior? that happens a lot, and is pretty normal.
IF there was a problem, I think the IO would have told you what you need to correct it ..or they will send you a letter...?
so, unless that happens, I don't think it makes sense to worry so early.
I think you should just wait a reasonable amount of time, and if you don't hear anything and/if you're worried, then make an infopass..
But you probably will be ok, esp. because you said the IV went "smooth".
(I am also surprised by the amazing number of people who get this notice at the IV, but do not try to ask the IO "why?", even when they have the chance, esp. when it's the IO who hands them the N652, as in some cases...you may not have had the chance, i don't know)