Someone on Reddit figured out this particular ID is used by Gmail on Android. (This does not answer the question of how to find out more about any such ID in general; I’m not sure there is a way, as there’s nothing about this one in the cloud console either.)

Note that when called without arguments, this yields the value of $0, which may not be what’s intended.

I’m facing the same issue consistently with Whooshkaa URLs, for example: https://player.whooshkaa.com/episode?id=330009

If your theme has a searchform.php, you’re probably hitting Ticket #16541: get_search_form() ignores $echo if searchform.php exists.

Your workaround is fine if you’re just echoing the search form anyway, but if you need to capture the output in a variable, you can work around this with output buffering:

<?php ob_start();
get_search_form();
$my_search_form = ob_get_clean(); ?>