Look at the dates; we are talking about two different things here. The second pilot "Where Man Has Gone Before" was filmed in July 1965 and the memo is dated April 1966. At this point when the memo came out the pilot "Where No Man Has Gone Before" had already been filmed. That memo is talking about props for the series after it had been approved for production. The phaser rifle that we know had already been used in the second pilot but apparently there was going to be design changes (like the changes made to the hand phasers and communicators for the series) to the phaser rifle for the series. As some point it was apparently decided that they wouldn't need a phaser rifle for the series.