It might be that the 30% reported is 30% of one of the 4 cores the Nexus 4 has. When all 4 cores are busy it might be that the value reported by top for that same operation would be 30/4.
It might be that the 30% reported is 30% of one of the 4 cores the Nexus 4 has. When all 4 cores are busy it might be that the value reported by top for that same operation would be 30/4.