New players being called bots

Whether your playing a bot match or a regular pvp match, why is it that people will label you as a bot script if you die even if your just new to the game, champion, or role?

I just had a game where one guy was being toxic to his team member because he/she was not performing well(at least to the degree he wants). So he spammed in chat to end the game quickly while grieving over his teammate being a bot. He stated that this player "just auto attacked", which is not true because i saw that player use their spells and understand how they were suppose to be playing that champion. However since they died alot he/she was labelled as a intentional feeder too.