Miller has one notable injury before he was drafted, the grade 2 MCL Sprain in his knee in the 2022 CFB semi final.
That's an injury, not a continuing pattern of injuries.
The medical team on each NFL club obviously has to make recommendations about ability to rehab existing injury and propensity for future injury, and the Saints clearly thought rehabbing a grade 2 sprain was minor enough to take him in the third.