The directory structure of Magento in a Bitnami cloud image is in
/opt/bitnami/apps/magento/htdocs. In this image, the "Default" Magento theme mentioned in the article is in
/opt/bitnami/apps/magento/htdocs/app/design/frontend and the custom package should be created in
Keep in mind, though, that Magento2 removed the "skin" directory among other changes, so the article you were following is perhaps outdated.
Hope it helps.