Blue Pentagon just means it's Kalos native, so Steelix (or Onix) was hatched in a XY game.
Being in a Heavy Ball just means that one of its ancestors was caught in HGSS and transferred through to XY, since the new breeding mechanic in Gen VI allows the female Pokemon to pass down their Pokeball designs.
As for its stats, check here. From what I can tell it has its attack EVs maxed out.
6 perfect IVs is not that uncommon nowadays with Destiny Knot allowing offspring to be guaranteed 5 inherited IVs from their parents. Getting 6 perfect IVs, while rare, is not impossible.
tl;dr - if it doesn't have hacked moves/ ability then there's no reason to believe it's hacked.
