You need to reset the IFS variable (the delimeter used for arrays).
OIFS=$IFS #save originalIFS=','df -h | awk '{ print $5" "$6"," }'
You could do this in Bash without awk.
array=()while read -a line; do array+=("${line[4]} ${line[5]}")done < <(df -h)
You may use this:
eval array=( $(df -h | awk '{ printf("\"%s %s\" ", $5, $6) }') )