Presented in the manner the way the article did, this looks really bad and while it's not good, it's not all that terrible.
There are 31 teams in the NFL, each with an active roster and practice squad equal to 61 players per season. That's 1,952 players per year. For the almost 14 years included in the report the 640 arrests represents only 0.23% of the 27,328 players in the league.