I think that this angle is set so that person standing near the table would look at the display at 90 degree angle, just like with general monitor setup advice

I think that this angle is set so that person standing near the table would look at the display at 90 degree angle, just like with general monitor setup advice (monitor perpendicular to the line of sight, line of sight ends at the top border of the display). Since people are standing, not sitting, then notebook display should be a bit tilted backwards.