Translation:He did not carry the bag on his back.
"I hā'awe" is past tense. The "I" denotes past tense before the verb. The sentence you wrote isn't grammatically correct. "Ua" would only be used at the beginning of a sentence (in the Po'o) to denote past tense. When it comes later in the sentence, "I" is used instead of "ua." I do agree that the sentence is translated to "the" back rather than her/his back.