Just a slight correction to your description: its the MOBs that are in background mode and not the text. The font is always drawn in the foreground colour (using colour stack mode) on the HSC league table screen.
Although the additional technical detail is welcomed, I believe he meant that from a less technical perspective: The text is drawn on the BACKTAB (i.e., the screen background) but it's the MOBs that appear behind them. In other words, the first assumption people made on seeing it is that the floating text in the foreground must be MOBs, but they are in fact "drawn in the background" as it were.
Anyway, clever trick indeed, and very impressive in practice.