The demonstrator mentions, several times, putting the keyboard into "Full Range" or "Full Keyboard" chord detection mode. When this is done, the Auto-accompaniment split-point is turned off, the right hand voice(s) is/are spread across the entire keyboard and notes across the entire keyboard are used to determine the correct Auto-accompaniment chord, rather than just those to the left of the split point. Basically, it allows the player to use Auto-accompaniment while being able to play across the entire key range, like a real piano.
The PSR "E" series (and their EW300/400 76-key siblings) do NOT support "Full Range" or "Full Keyboard" mode. To have that feature, you have to get into the higher priced PSR "S" series models, or some of the older PSR models, such as the PSR-1000/1100; 2000/2100/2200; or 1500/3000; or even the much older PSR-8000/9000, or any of the top-of-the-line Tyros models.