The troll has "giant racial hit dice", defined by the characteristics of the giant type. In this direction, Yes, giant is very similar to a class. Like class levels, racially successful dice, or RHD for short, are hit dice– and your overall character level is actually based on your total number of dice, so class level (if any) plus driving right (if any).
It is this general character that determines when a creature gains feats. They are not premium exploits, but regular feats that each creature (with an Intelligence score) wins at 1st and then at every level divisible by 3. As the troll has 6 RHD (and no class level), he gets three feats, one to every 1st, 3rd and 6th. Manuel Monster VReferences to Lightning Reflexes, Multiattack and Power Attack indicate that these three exploits are the typical troll blader selections for these exploits.
A premium A feat is a feat that adds to the achievements you get in the 1st rank and levels divisible by 3. For example, those awarded by the classes fighter, monk or ranger. Or, for example, the exploits of arms control granted by the elvish race – which would be racial bonus exploits. What are you polymorphous to be able to give you.
The bladder troll has no bonus, racial or otherwise, but only the three bonuses he is entitled to as a creature with 6 HD. You do not get that as bonus feats.
The bonus exploits are shown in monster statistics blocks with a B. If monster stats include class levels, you'll have to double check that these bonus feats are not those, but for most monsters (without class levels), a bonus feat must be a feat of race, like a feat. Monster would have no other source of prowess.