Teaching others about Bitcoin is already a big contribution to Bitcoin since you will bring more people to use Bitcoin and adopt its technology/usage.
There’s a lot of different contribution on Bitcoin not only through investing on it. A simple encouragement or support to Bitcoin that will engage to non Bitcoin holder is already valuable use of your time.
It’s just hard to believe someone preaching and doesn’t follow what he is teaching. It’s like you already have a genie that can give you wealth but you don’t use it.
I think his talking about the person in particular,
Yes other people will benefit from the knowledge, but imagine others making money with the use of your knowledge, but you on the other end isn't making money, your just like a teacher without payment.
So it should be an encouragement to these sets of people to take a bold step and start investing and using the knowledge for their self as well.