Essentially true if you use an Taifun's File extension and build for Android. Here is a discussion
How can I make it so that music (mp3 files) can be played from the external SD card, whether directly or indirectly? that is a bit complex and convoluted.
What you need to do depends on which Android version you are using. The simplified instructions that are contained in Taifun's File extension documentation might work more or less as written App Inventor Extensions: File | Pura Vida Apps . Wish I could be more helpful; many things have changed recently with App Inventor and Googles requirements for coding. Player works; File Extension is necessary to properly locate where the music files are on your Android or it might be possible using the new File component that is part of nb187 (the latest App Inventor release).
Try something; if you run into issues, ask again. 