Spinal stenosis basically means that the spinal canal is narrower than normal. If it is narrowed to the point that it impinges on the spinal cord and roots that run through the canal, it can cause a ton of issues ranging from numbness to pain to lack of coordination and balance. There are also several other complications that can make it more serious. At the cervical level (i.e. at the neck, where it's reported with DGF), it can be caused by herniated discs, so that may be how the discovery of a herniated disc led to the discovery.
The doctors in SC's article were saying that it hasn't been proven to increase risk of spinal cord injury and it doesn't mean you can't play football, but I found a pretty good article whose authors believe there is a correlation with SCI and strongly advise that their patients don't play football.There was another study that found that 5% of the ~3000 players that attended the NFL combine from 2003-2011 had cervical spine injuries, including ten cases of stenosis. All 10 were drafted and none had spinal cord injuries as of 2016. However, players that did suffer spinal cord injuries were more likely to have narrow spinal canals.
It seems like overall there isn't much of a consensus on how much risk stenosis poses to athletes, how it should be treated, or when they are safe to return to their sport. Spinal cord injuries can be really catastrophic so I think that it's understandable why any increase in risk can be quite a deterrent.
I'm not a doctor and I haven't seen DeGabriel as a patient, so I can't/don't want to speculate too much about his future.