Does open-source mean it's free? I don't think that is what it means, it just means the source is open, viewable, and you are free to use it as per the licensing.
If it's open source, people are free to redistribute it. Copies of open source software can be sold for money, but open source licenses allow redistributing the software for free. In practise, that means most people won't buy the open source software from a seller, they will choose instead to get a copy from someone who is willing to redistribute it free of charge.
