Initially bitcoin was created for everyone as a solution to eliminating the need for any third-party or financial institution, but due to its volatility it pleases people to see it as a store of value of which has been profitable to a lot of lot of holders. Irrespective of the fact that alot of holders have been profitable from their holdings, it doesn't justify that bitcoin is safe or profit is guaranteed. Alot of people like to consider the merits without considering the demerits and that is why we often hear people call bitcoin scam, or tag bitcoin to those shitcoins probably because of their performance without properly understanding that bitcoin is entirely different any project that seems to have thesame form. So yeah the poor can invest in bitcoin but the most important thing is to have a source of income to fuel their enthusiasm and accumulate using any strategy that suits them but most recommended the DCA strategy. However If anyone wishes to invest in bitcoin without a steady source of income, I'll advise they get a job first because investing without a source of income is easily predictable that they'll end up spending back their investment if problem arises.
Even if they get a source of income then they should also understand the concept of risk management and consider investing only from their discretionary income so they don't make mistakes of using money for other important need to invest in bitcoin and later go back to make withdrawal when they realize their mistake or when the need becomes extremely demanding.
Bitcoin started as way for everyone to send money without needing banks or other companies. But because its price goes up and down much people now mostly see it as something to save money in hoping it will be worth more later and it has made money for many people who have held it. It is true that price has gone up for those who kept it for long time and this makes people sometimes forget about the risks.
Warning you gave people is also good, not to think Bitcoin is always safe or that they are guaranteed to make money. Fact is that its price changes much and only looking at times it has gone up without thinking about times it could go down is bad way to think. This only looking at good sides is probably why some people especially if they have lost money on other cryptocurrencies wrongly call Bitcoin is also scam or think it is same as those less trustworthy coins without really understanding that Bitcoin is very different.
Having steady job and income is most important thing before even thinking about putting money into something as unpredictable as Bitcoin. If you do not have regular income you will be very tempted to sell your Bitcoin if you have any money problems and that mostly leads to losing money. And idea of buying Bitcoin regularly with DCA is good way for many people because it helps reduces risk of buying at wrong time and encourages thinking about it as long term investment.