The information in this article is out-of-date and is only being retained for reference purposes. For more current information, see here.
If you have sync your Metamask mobile app with your extension but Binance network is still only visible in the extension, this is expected behavior for now.
Indeed you will need to add Binance network as a custom network in your mobile app and also add the tokens manually.
Additionally, we encourage you to check out other feature requests users have submitted and upvote the ones you would like to see implemented.