One of the things parents deal with (as everyone on this site will attest) are people who have no idea about diabetes and relay poor information, obsolute information and just do not have all facts. I have a brother in law who used to tell me about this person or that person with diabetes so I would ask "did he have type 1 or Type 2, When was he diagnosed, what medcines is he on etc. The answers were obviously "I don't know" and that is when I say "right - you don't know - you can't put every person with diabetes the same catagory.
Yes, we have people here who have had diabetes for years (yes even over 50) and those who struggle (like my 15 year old son).
The person who told their dad died at age 50 also needed to tell you when he was diagnosed -was it early in life or a few years ago, was he type one or type 2, did he manage his diabetes well, was he seeing his endo, was he on the pump or MDI, if he was type 2 was he exercising and watching his diet etc.
Those are the questions that need to be answered. Yes, there are complications to those who do not manage well and over a long period of time and you should be aware of them. We need to pay attention to those things so we can better manage the here and now.
ITs hard enough being a parent without the know it all's in our life.
Next time it might happen then ask those questions, there might have been a very valid reason and it more than likely had to do with long term poor management. .
Or, you can be direct like I have learned to be and tell them " those stories don't do anyone good - if you know anyone else please do not tell me">
Best of luck - the best way to avoid all those issues is to care and the fact that your hear looking for answers shows you do.