One is for general faction use, and the other is produced just for Steel Song. You can't really see it, but there are a number of very large target markings on it, and there are also a few torpedo-attraction-beacons (TABs) included in the superstructure of the hull.
Since you are bringing up the issue, I also saw two different Pirate Battlecruisers during the last community challenge. In this case they have different images and stats too. Funnily, how the name is centred on screen is different too.
ST2 Alpha - HuaWei P10 Plus, Build VKY-L09 220.127.116.113(C654), EMUI 8.0.0, Android 7.0, res 2560×1440 [Not in use: ST2 Alpha - iPad 2(?), Model MC980C/A, OS Version 9.3.5 (13G36)]
In all seriousness, what may have happened is that Cory tweaked/changed the ship design and graphics during an update. The update only affects new ships, not ships that you already own. It's one of those things specific to ST. If you find the older design better than new, keep it, otherwise if the new is better, do the trade in.
Cory's already advised he's modified a number of ships - and this is something he does periodically in order to readdress balance issues.