Analogy is not always correct
TeamTAD is an open source movement. However the focus is on architecture and not on software. TeamTAD could use commercial software (and other commercial stuff) to do its activities along with FOSS (Free/Open Source Software). An open source programmer may go out and buy his own coffee, computer and other tools for his trade, along with some free open-source tools that he may use on his computer. Similarly, at TeamTAD too you could consider paying for some of the services/solutions built around it (however it is a promise that all software tools would be free).
Some of these solutions are free and some are commercial. If you read Richard Stallman's excellent article that defines the word "commercial" you would be convinced that using commercial work has no correlation with freedom.
We just want to make a point that architectural information should be as clear, usable and re-usable as possible. That is the only real analogy that we seek to make
TeamTAD is not asking you to necessarily do you work free of cost but we do want your work to be easily readable, understandable and the representation of the work (i.e. its source code) freely available in times to come. We want architecture to be bereft of obfuscation -- which in simpler English means, years from now people should truly understand your designs and its intentions even when you are not around.
In certain situations, it is important that the source code of the architecture being designed is NOT kept open. For e.g. It may not make sense to keep the design of a jail or an embassy in an open manner. That said, even such designs would need to be plumbed for information and simulation at critical times; say during a fire, a prison riot or a terrorist attack. At such time, the data would need to be shared to a wider set of experts (a prison riot expert may need to look at the details of the prison, for example). Hence data should always be in a position to be openable even if it is not kept open right from the beginning.