Pulling a GPC variable

[Dr.CustUmz]

var_dump($_REQUEST);

PHP Code:

C:\wamp\www\admincp\digigacpacp.php:445:
array (size=6)
  'do' => string 'editproduct' (length=11)
  'productid' => int 1
  'explain' => int 0
  's' => string '' (length=0)
  'styleid' => int 0
  'langid' => int 0 


var_dump($vbulletin->GPC);

PHP Code:

C:\wamp\www\admincp\digigacpacp.php:444:
array (size=17)
  'explain' => int 0
  'vbulletin_collapse' => string 'thanks_postbit_64993
cybchatbox
drc_registration_booster
file_templates
shat_zodiac
g_answer_forums
ajax_live_box
ckeditor_edit
forumtitle
extra_threadfields
c_news_letter
g_forumhome_tabs
toplist
invitation
ico_content
livetopic
smnlikquick
gntb
thread_listing_bgcolors
vbclassified
data_interactivehome
throttle_posts
sqrtboyvbttv30
auto_close_threads
blackcat_download_images
latest_posts_blackthorn
chgtpowner38
threadprefix_changeinline
vox_close_threads
rellect_closed_prefix
hideimg_guests
lastest_thread_'... (length=1091)
  'devreferrerid' => int 0
  'devuserid' => int 1
  'devpassword' => string 'd13a309e18a79b8af634fb0477fbc687' (length=32)
  'devlastvisit' => int 1603165768
  'devlastactivity' => int 0
  'devthreadedmode' => string '' (length=0)
  'devsessionhash' => string '6106f9e943c802d63d795c67ff4d9649' (length=32)
  'devstyleid' => int 2
  'devlanguageid' => int 0
  's' => string '' (length=0)
  'styleid' => int 0
  'langid' => int 0
  'adminhash' => string '' (length=0)
  'devcpsession' => string '16618cfe2c0626479f03c1f80d7abab7' (length=32)
  'productid' => int 1 


I am a bit baffled why there are references to products I have not installed on this fresh install, The only product I have installed is the product I am working on.

This is the portion in my page where the productid and catid are added, I have stripped a majority of this page but kept what should be relevant.

PHP Code:

if ($_REQUEST['do'] == 'doaddproduct')
{
    $vbulletin->input->clean_array_gpc('r', array(
        'catid' => TYPE_UINT,
    'productid' => TYPE_UINT
    ));

    $db->query_write("INSERT INTO " . TABLE_PREFIX . "products
        (catid)
        VALUES
            (
                " . intval($vbulletin->GPC['catid']) . "
            )
    ");

    $db->query_write("UPDATE " . TABLE_PREFIX . "categories
        SET products = products + 1
        WHERE catid = " . intval($vbulletin->GPC['catid']) . "
    ");

    print_table_start();
    print_table_header($vbphrase['digigacpacp']);
    print_description_row('<strong>' . $vbphrase['done'] . '</strong>');
    print_table_footer();

    print_cp_redirect("digigacpacp.php?" . $vbulletin->session->vars['sessionurl'] . "do=viewproducts&amp;catid=" . $vbulletin->GPC['catid'], 2);
} 


I guess I should be asking is, how is a GPC variable even created? Because I know I can use productid on numerous pages, although I am unable to use catid on these pages.