inability to use streaming mode for retrieving query results

I may be misunderstanding the documentation but
I was expecting that this code would show different timestamps:
$ php -a
Interactive shell

php > $query="select id, (select count from dropbox2002_202606.focalfollow where focal = b.id and endtype='END') nff from capuchin.biograph3 b having nff>0 limit 9";
php > $mysqli = new mysqli("localhost", "root", "", "dropbox2002_202606");
php > $uresult = $mysqli->query($query, MYSQLI_USE_RESULT);
if ($uresult) { while ($row = $uresult->fetch_assoc())

}
php > php { 2026-11-05T21:04:59+00:00AM
2026-11-05T21:04:59+00:00AN
2026-11-05T21:04:59+00:00AR
2026-11-05T21:04:59+00:00BE
2026-11-05T21:04:59+00:00BK
2026-11-05T21:04:59+00:00BL
2026-11-05T21:04:59+00:00BX
2026-11-05T21:04:59+00:00CG
2026-11-05T21:04:59+00:00CL

The query, when run with different limits, takes different amounts of time, roughly proportional to the limit, e.g., limit 1 takes .265 sec, limit 4 takes .73 sec, limit 9 takes 1.497 sec.
And explain of the query returns, as expected, b as primary and DEPENDENT SUBQUERY for focalfollow.

So what am I missing? Is this a bug in php? Mariadb? (I never got it to work in mysql either)