(including the secret armed base at 7.4), while puzzling, is not greatly inconsistent with the Kilrathi character, particularly in the light of the recent resurgence in ancient clan rivalries.
What is both puzzling and troubling is the question of whether the Kilrathi (assuming they are Kilrathi) may have got the previously unknown jamming technologies and formidable destructive potential inherent in the presumed and confirmed attacks, as well as a possibility of a previously unknown jump technology. The anomalous artefact from Kilrah 7.4 is also disconcerting. We are led inexorably towards a third scenario.
If an unknown race is, in fact, involved in the attacks, that raises further questions.
As to their biology, the only data available is the ‘hand-print’ on the artefact recovered at Kilrah 7.4. If this is indeed what the shape represents, and not some sort of writing or art, the impression is of a remarkably flexible tool-using appendage, larger than a Human hand and possibly even stronger than a Kilrathi claw. The hypothetical appendage, while possessing the approximate functionality of a Human hand, does not conform to the morphology of any known alien species.
Nothing can be stated about their psychology, except that the thoroughness and efficiency of the attacks suggest a remarkable degree of organisation and co-operation. Machine intelligence, or some sort of hive-mind, would not be inconsistent with current data.