It has long descenders and ascenders which make it easy for dyslexic readers to differentiate letters. Dyslexic readers also find handwritten looking fonts easier to read because they are more familiar with that style.
Probably in part due to them being less symmetrical. "bd" are almost identical in the font on HN, but mirrored, while in handwriting you form different connection angles because you write them differently.
I was curious about this, as well - from the links, it sounds like dyslexics rely more on the shape of whole words when reading, so fonts with pronounced ascenders and descenders (the stems and tails on t, j, etc.) may be easier to read.
The opposite extreme would be WRITING IN ALL CAPS in a fixed width font, making every word into a rectangle.