I agree with you that he was actually referring to diversification but we can only talk about diversification when your investment n Bitcoin has not yield any profit in the long-term, in such situation an investors may decide to try new things to know if they will be better than the existing one, although people can still diversify their investment when they have achieved a bulky portfolio or when they have attain a certain level of wealth but thats not always the case, investors are always looking at investments that add values with good potentials, am not against diversification but i somuch believe in Bitcoin and i think we shouldn't be skeptical about this digital wealth, for me am not diversifying anytime soon because I have not gotten a sufficient portfolio yet, for now my major concern is to keep accuamulating the little i can contimously without allowing any form of discouragement in my way.
The fact that someone is a Bitcoin investor doesn't mean they can't diversify their investment to other portfolios, so far the funds in there and they've a acquired knowledge about a particular investment then they're good to go, Bitcoin is not the only good investment, there are still others that could yield good profit for people on the long run.
However, I agree with you that Bitcoin is currently one of the best investment anyone could think of for long-term purpose, it has proved over time that it could yield great profit for people in the future so the best decision anyone could take is investing in their future through Bitcoin without any doubt about it. Also I think you'll be making the the best decision to accumulate as much as you can without any discouragement then you can diversify to other investment when you've made profit from it in future.