The interrupting capacity is the headline here: 187 kA at 240 V, 121 kA at 415/440 V, 75.6 kA at 500 V, and still 3.7 kA at 690 V. That's serious fault-clearing muscle for a 100 A frame.
The 100 A continuous rating is the load it handles without tripping — sized for a feeder or a large motor branch. At 690 V the 3.7 kA is lower, but that's typical for a 100 A frame on a 690 V system — the application voltage drives the rating.
The 86 mm depth leaves room for rear-connection bus bars or a gland plate behind it in a shallow enclosure.