555 BST is unusually high for a fossil pokemon without a debilitating ability. Unfortunately that's not exactly an ideal spread for such an offense-oriented type.
I'd certainly tend to agree with you, but it's because these are just estimates, we have no idea what their IVs are, or how many EVs they've been trained on. I calc'd the second Aurorus (
http://instagram.com/p/fQLN5boBeA/#) and got a lower spread:
110-115 / 85-90 / 65 / 95-100 / 95 / 70 for a 525-530 BST.
So who knows, maybe the first one had way more than the 16 IVs and 60 EVs I was assuming. I used 68 EVs for this second one.
But Tyrantrum was already calculated to have a 555 BST either way, so these calcs are obviously not set in stone just yet. On the plus side, X and Y are so close I can smell them now...