That wouldn't be considered tampering with the evidence because even if the incident was properly reported, the gun wouldn't have been left at the scene.
Ramos didn't tamper with the scene like Compean did.
You might as well say that Ramos shouldn't have removed himself from the scene.
By not reporting the incident, Ramos violated regulations, but his were acts of omission rather than consciously destroying evidence.
Both are wrong, but one can be considered a crime, while the other tends to be a work disciplinary issue.