Some bosses on HM drop random rakata tokens, but if you do NM mode they automatically drop rakata. It's a very slim chance for the HM to drop the rakata piece so you got very lucky.
No its not.
You'll get the Rakata pieces every time, *unless* you have ML on which screws your drops.
Protip: Dont run with ML on, you'll find your loot increases by alot.