I'm just trying to get things straight.

I've assembled my genome by mapping the sequence reads to a reference genome. Then I got this mapping statistic:

Since the unmapped reads was rather high, I'm trying to figure out what they was by investigating their taxonomy using kraken2.

$ kraken2 --use-names --threads 4 --db minikraken2_v2_8GB_20200312 --fastq-input --report evol1_NSN --paired NSN.unmapped.R1.fastq NSN.unmapped.R2.fastq > evol1_NSN.kraken

And when I viewed the report using pavian, I got this

So here's the question, the total unmapped reads based on the mapping statistic was 12,999,627 reads. But the number of raw reads investigated (the red highlighted box) was 6,473,047 reads. So the differences in the number is it because kraken2 has the "--paired" function? Or else I can't explain why only half of the unmapped reads were investigated for their taxonomy.