In psychology, laziness simply does not exists as a mental health issue or as a personality trait.
It's a vague and judgemental word used to describe a behavior while the real cause might be burnout, depression or many other.
Laziness isn't vague, nor judgemental. Laziness is marked by non-production. Which can be measured by simple time-tracking. How many hours a day is he coding/writing vs. on YouTube "passing the time".
Moreover, the post specifically says "symptoms". And he's attempting to discern between the words, specifically asking "What's the difference between..."
What you described is not laziness but either a lack of focus, a lack of awareness of how you are wasting your own time or a conscious decision to not do your work in favor of something else. Both depression and burnout make it hard to focus on tasks that are going to move your life forward, so you could easily be depressed or burnt out AND waste hours on Youtube as a result of it. You could also just be a distracted individual who is not burnt out or depressed and still waste time on Youtube. You could be too tired to devote your mind to coding, so you waste time on Youtube - this is just biological reality, and I dont think we would normally call someone lazy if they can't code anymore after a 12 hour day. Perhaps the act of coding brings about some negative thoughts (e.g. why am I doing this, my colleagues are just going to criticize my commit) so you're actively avoiding it in favor of another activity. This is not necessarily lack of focus but maybe a lack of awareness. Perhaps you are feeling stressed and watching Youtube helps you relax, so it is a strategy to help you avoid burnout in the long run. Basically, I don't think laziness exists, its just a word used to describe something you don't understand.