Because, the text was made a minute after Jaztremski appeared on television for an away game. It was in Green Bay. Jaztremski never handles balls at all after they are given to refs. That is left to McNally, who is the self-described deflator. NFL procedures have ball boys from the home team handling the balls after the refs pump them up. The Patriots guys were nowhere near the balls, neither Jastremski nor McNally who was 1,000 miles away.
The deflate/deflator excuse sounds preposterous. Which is why the Patriots wouldn't want to emphasize it. That being said, there were 3 texts about deflation. This one during the Green Bay game couldn't have referred to footballs. The "deflator" text in March could have. The third "deflate" text actually exonerates Brady because Brady had to be told that the refs inflate the balls, which is why Brady told Jaztremski to "show 'in rulebook."