Drew Brees is not the tallest quarterback in the NFL. Some teams devalued him in the draft because he was shorter than what was optimum for most NFL teams to draft. While a little bit taller, Garrett Grayson fits a similar mold in coming from a pro style offense at Colorado State to go to Sean Payton's NFL scheme with the Saints.
There was not a lot of proof that there was a clear third quarterback in this draft class, but the Saints went with the young man who played against lesser competition in the Mountain West, but with a better system to adjust to a professional offense. Grayson is known for having a good deep arm, but Brees should still be there in New Orleans for years to come, which give the Saints' coaching staff time to develop in order to keep having strong talent on the field for when Brees should depart.
Grayson was awarded the 2014 Mountain West Defensive player of the year and holds school records for many different passing accomplishments. He didn't come out of nowhere, but many others might have been expecting to see someone else like Bryce Petty perhaps. But in the Senior Bowl, where many NFL teams can do some quality scouting, Garrett Grayson went 8-15 for 115 yards and that might have just pushed him over the edge with the Saints scouts and staff.