Mapping statistics from bam file using bbtools and sambamba
Try samtools flagstat or sambamba flagstat to get similar type of information about your bam file. It may be easier to interpret. Both of these tools can be installed using conda if needed.
EDIT:
Yes, the results of sambamba flagstat you showed in your edited post indicate exactly what you said: 94.91% mapped and 100% - 94.91% = 5.09% unmapped:
64035749 + 0 mapped (94.91%:N/A)