That could indeed be referring to the internal 8GB storage. EMMC is flash memory and controller on a chip.
8GB isn't very much and will fill up fast, especially in 4K. In 4K that gets you probably about 13 minutes record time.
Do you have a U3 rated SD card installed? If so, did you select to use the SD instead of the internal storage in the app?
To get the contents of the internal storage, you'll need to connect your AC to your PC while AC is powered on. You may also need to install Assistant in order to install the needed driver, even if it is probably presenting itself as typical USB mass storage.