Ok, just checked.
Some words we know, but some we don't understand. "Kes" is indeed there to turn the verb "Zustak" to the past tense.
"Milok" could be the pronoun "we/us". It's usually "Milon", but it was also used as "Milo" once, and since the language canonically has a lot of variation, this could be one such case.
"Ru" isn't a pronoun, but the gender particle for the "10th kind", the gender used to describe a "stable land or country". We had never seen the 10th kind particle used in place of a pronoun, iirc, but the 4th and 3rd kinds' particles can be used this way.
"RIEHA GARMILLAS" means "planet Garmillas".
So, I think we can extrapolate that the translation would be something along the lines of
"ROFFOK (presumably an insult) Dezariam, you ZUSTGAK-ed us. We (are) planet Garmillas."
Note that the verb "to be" seems to be omittable in the Garmillas language. Sooo the only thing we don't understand here is "Zustgak", it might mean "destroy" as you said, or maybe it means "kill" or something like that.
