Too many people in the world worked for a while, and while working, also invested in crypto on the side and I believe that's what he is talking about? Not entirely sure to be fair, that's what I assumed, and it's not a job, it's investment so you are right that we can't call it a side job but not everyone speaks English like it's their native language so some people may make those kind of mistakes.
It's true that if you have a normal work, like you go 9 am every day, get out at 5pm every day, that kind of job, then yeah I agree that having crypto investments on the side, check them out when you get home before dinner, is the best method. Let's say you get out of your job at 5pm, at home by 5:30, and eat dinner by 7 pm, there is 1.5 hours left for you before dinner, then you can spend that checking out crypto and making investments. You can keep doing it after dinner too, but I think 1 hour give or take everyday is enough, no need to be obsessed about it.
No doubt BTC is side line investment but that is not like that of other investments. Other investments can not give you returns like BTC . We will remain happy if we invested in BTC . But there is also Sol and BNB are present and these coins have capability to change lifestyle. We can improve our life style by taking interest in cryptocurrency because BTC future is bright.But there is also gold in which you can invest but gold can't give you returns like BTC. But I'm long run it can give you profit. If you are skilled person you can start your own business and you can make your outlets and you can be successful.