The warning kind of feels like if you follow what it says, then the achievements that follow will not be missable. However that does not appear to be the case when reading why those achievements are missable later in the guide.
Not a big problem, but might mess up somebody that thinks "I'll just play for fun and as long as I pick option C, I'll be able to get all the achievements." Personally that's what I was thinking, but decided to double check just in case.
Completed Games - 39 Retail - 40 XBLA - 29 WP7/8 - 6 W8 - 2 X1
Most Recent: Guacamelee (X1)