strange CREATE INDEX tab completion cases

These two tab completion pieces look strange to me:

/* If we have CREATE|UNIQUE INDEX <sth> CONCURRENTLY, then add "ON" */
else if ((pg_strcasecmp(prev3_wd, "INDEX") == 0 ||
pg_strcasecmp(prev2_wd, "INDEX") == 0) &&
pg_strcasecmp(prev_wd, "CONCURRENTLY") == 0)
COMPLETE_WITH_CONST("ON");
/* If we have CREATE|UNIQUE INDEX <sth>, then add "ON" or "CONCURRENTLY" */
else if ((pg_strcasecmp(prev3_wd, "CREATE") == 0 ||
pg_strcasecmp(prev3_wd, "UNIQUE") == 0) &&
pg_strcasecmp(prev2_wd, "INDEX") == 0)
{
static const char *const list_CREATE_INDEX[] =
{"CONCURRENTLY", "ON", NULL};

COMPLETE_WITH_LIST(list_CREATE_INDEX);
}

They appear to support a syntax along the lines of

CREATE INDEX name CONCURRENTLY

which is not the actual syntax.