It's not uncommon for teams to use their bye week as a time to keep track of their "emergency list" players, which may be the motivation behind bringing in some of the players who worked out.
Powell and Malone have AFC East ties, as they were released by the Bills and Jets, respectively, earlier this season. Cain is a UMass graduate who has been with numerous NFL teams, while Jennings spent 13 seasons with the 49ers. Carlos Maltos, a native of Mexico, spent part of this past offseason with the Saints.
Mattes has had multiple tenures with the Patriots after being signed as an undrafted free agent out of North Carolina State in May. He was most recently released by the team from injured reserve on Aug. 24, though his workout suggests he has recovered from the injury.