The general rule for Bonus Feats is in the Monster Manual - Reading The Monster Entries:
All the requirements to have the prerequisites - like in the case of Fighter's Bonus Feats - are exceptions from this ruleFeats
The line gives the creature’s feats. A monster gains feats just as a character does. Sometimes a creature has one or more bonus feats, marked with a superscript B (B). Creatures often do not have the prerequisites for a bonus feat. If this is so, the creature can still use the feat. If you wish to customize the creature with new feats, you can reassign its other feats, but not its bonus feats. A creature cannot have a feat that is not a bonus feat unless it has the feat’s prerequisites.