My opinion is that he used drugs. There's not enough information but think about it. He's a gamer and also a student so he's used to taking stimulants. Giving that he played for so long now it's reasonable to assume he did so in the past as well. Since he's also a student I'm assuming he had to keep up with his exams and such but at the same time he was also an avid gamer, so he had to find a way to keep up. Coffee gives you only so much. Other, stronger stimulants like cocaine give you way more of a boost.
He probably used cocaine regularly so as to keep up with his life style of being a student but also a hardcore gamer. Cocaine is known to increase the risk of heart attack and stroke and these are the only two possible reasons he died so suddenly.
Sure, there might have been an undiscovered heart disease but let's face it. In this day and age we can discover any anomalies present in the human body. If he had a heart disease he would've shown symptoms felt by him but also seen by others. If it was a rare condition that had minimal symptoms he did not consider serious then yeah, that might have been the cause but I'm under the assumption that these things usually start affecting you after the age of 25 and/or under specific condition. He's a gamer so he pulled a lot of all nighters and spent many nights not sleeping and since he managed to keep up this life style since he was younger we can safely cross heart disease from the chart. There's always high blood pressure but this disease is rarely ever present in young people and usually there's an underlying reason for it like obesity, excessive smoking, excessive drinking etc. and usually problems start appearing after the age of 40.
Since we crossed heart conditions from the list the only other alternative for such a sudden death is stroke. He either had a problem with clots or an abnormal structure of his veins that would've caused a rupture. If he had blood clots he would've had symptoms before since this disease is genetic. The same goes for an abnormal vein structure. At 19 you're technically quite close to becoming a fully fledged adult. If there was a problem it would have appeared at a younger age.
I can't see any other alternative other than drugs. Then again, I'm not a doctor and everything I've just talked about I've done so using information read from the internet and we all know how reliable that is.
My claim still stands. I cannot see any other reason but drugs.