Rugby turned pro in 1995. So the "amateur era" is likely referring to players pre-1995. While not strictly "pro", they were not your typical rec league players

Rugby turned pro in 1995. So the "amateur era" is likely referring to players pre-1995. While not strictly "pro", they were not your typical rec league players. They were doing international tournaments and playing for national teams, etc... From what I have read, the evidence really points to duration of exposure as the key risk factor. So for someone who plays at the amateur club level, typically practicing 1-2 times a week, the risk might be fairly low. They are probably racking up a fraction of the exposure that a professional would experience in a given year.