Correct, the first user you created is the admin user. On the emonSD Emocnms is restricted to a single user account. This can be changed by changing /var/www/emoncms/setting.php:
$default_language = 'en_GB';
// Theme location (folder located under Theme/, and must have the same structure as the basic one)
$theme = "basic";
// Theme colour options: "standard", "blue", "sun"
$themecolor = "blue";
// Favicon filenme in Theme/$theme
$favicon = "favicon_emonpi.png";
// Use full screen width
$fullwidth = true;
// Main menu collapses on lower screen widths
$menucollapses = false;
// Enable multi user emoncms.
// If set to false, emoncms will automatically remove the register form and
// ability to create further users after the first user has been created
$enable_multi_user = false;