While taking a backup of slave server with --slave-info option, it only contains gtid
information of master server but not binlog file and position.
As per the documentation,
"Mariabackup does not check if GTIDs are being used in replication. It takes a shortcut and assumes that if the gtid_slave_pos system variable is non-empty, then it writes the CHANGE MASTER command with the MASTER_USE_GTID option set to slave_pos. Otherwise, it writes the CHANGE MASTER command with the MASTER_LOG_FILE and MASTER_LOG_POS options using the master's binary log file and position. See
MDEV-19264 for more information."
so as per the code, if it will get value for gtid_slave_pos system variable, it will only mention gtid and not master log file and position. But actually, both details should be mentioned like
earlier. (OR xtrabackup does)