Its simple.
FEEDING is dying a lot.
But.....
When it comes to whats punishable you have separate just dying a lot from INTENTIONAL feeding.
Just dying alot is not punishable.
Intentional feeding is punishable.
People in lower elo are so quick to all chat in the chat to report someone just because they have a lot of deaths. If you watch higher elo streamers you do not see this happen unless the person is intentionally feeding. because they understand the difference.
if your top laner is 0/8/0 if you report him for feeding it most likely will get ignored UNLESS he either typed in the chat that he is inting or you can clearly see in the game that he is inting ...IE just running up to the enemy and standing there letting them kill him.
A lot of people get away with what they call soft inting. Which is basically inting but you make it look like you are trying and just playing badly. But people only do this when they either got in a argument with someone in champ select or during the game. if someone is doing this there is really nothing that can be done about it because you can not prove that they are not just playing badly and actually inting.
Also when looking at the game you are referring too......that game was a complete stop by the enemy team....every lane got their but kicked it looks like....you just happened to have the least deaths.