Thank you for your question.
I would suggest that the text "For any distribution ... deviations of the mean." is a displayed snippet of text and should be formatted according to the displayed material guidelines of Braille Formats, 2011.
The next chunk of text, beginning with "Example For any distribution, ..." does appear to be instructions preceding itemized material. The directive nature of "Find the fraction of all the numbers ..." especially makes me think this. So, I would suggest that the text beginning "Example ..." before item #15 should be formatted in 5-3.