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In essence I think what he's saying about investing with the amount any one can let go is because of the price movement of Bitcoin, it is not advisable for anyone to use all their life savings to invest in Bitcoin this does not mean that Bitcoin will disappoint you no this is important because the price may not be what you expect to see and to avoid panic and fear people are advised to invest with spare money and also don't depend solely on Bitcoin investment so that they will not regret when the price doesn't go up as expected.
The price of Bitcoin may have increased with time and since the declaration of Trump as the winner of US election there has been a massive increase in the price of Bitcoin thereby seeing Bitcoin move down 65k to 90k, the price is expected to hit 100k before the end of December but this is just the price prediction it may increase or go down with time.
You're right, we're still on the same point here. The point is, invest in an amount you can afford to lose, no matter what it is. Not to belittle bitcoin for being skeptical, but simply to control your real-world finances to have a more organized life. Moreover, Bitcoin itself has proven for decades that it is the best instrument in supporting financial freedom and avoiding inflation that occurs in FIAT.
This is first rule to follow for people want to invest since if they put high hopes and spend everything they have then they are one step to get broke if everything falls apart.
Investment posses risk so we should never have this gambler mindset where we put everything hoping to gain huge in return. Even if bitcoin is a good deal still we need to take precaution taking investment decision with this coin since price is so volatile and it takes good knowledge to understand on how it moves also what's best investment strategy we could able to use to increase our chance to earn with bitcoin.