Alter doesn't show in processlist

I'm performing an alter. It's currently running on a large table (300,000,000).

MariaDB [my_database]> ALTER TABLE my_table
    -> add INDEX a (x, y, z),
    -> add INDEX d (x);
Stage: 1 of 2 'copy to tmp table'   60.1% of stage done

But the processlist doesn't mention it, with repeated queries.

MariaDB [my_database]> show full processlist;
+----+------+-----------------+-------------+---------+------+-------+-----------------------+----------+
| Id | User | Host            | db          | Command | Time | State | Info                  | Progress |
+----+------+-----------------+-------------+---------+------+-------+-----------------------+----------+
|  6 | apps | localhost:52235 | my_database | Sleep   |  304 |       | NULL                  |    0.000 |
| 33 | apps | localhost       | my_database | Query   |    0 | NULL  | show full processlist |    0.000 |
+----+------+-----------------+-------------+---------+------+-------+-----------------------+----------+
2 rows in set (0.01 sec)

I would expect it to show up. Any ideas why not?