It's certainly possible to combine Joplin tags with inline tags. For example, have an article tagged with "!important", and keep specific paragraphs within the articles tagged with "!important". One way to achieve this is by using the Inline Tags plugin. With this plugin, you can write an inline tag in the text, and at the same time tag the note with the same Joplin tag.
Thanks for the feedback, I'll see if I can add support for Joplin tags in the next version.
The pseudo-tags that you see are tags that appear in your notes. You can click on them and see where exactly they appear in your notes. Even though you did not add them intentionally, they most probably follow the tag template and are therefore detected.