Obsidian uses non-standard Markdown for things such as block references, wiki-style links, etc. Since very early beta "export to standard Markdown" had been on the todo list so that notes taken in Obsidian would not be "locked in" because they were reliant on app-specific markup.
That being said standard Markdown does not provide notation for certain things, so it is somewhat up to interpretation how to convert certain features to standard Markdown.
