Is my understanding correct, or there is a nuance I do miss?
There may be several, but this one is important: free software grants freedom, but not to everyone. The four freedoms are granted to all legitimate users of the software. It is perfectly OK for some organisation to sell you a copy of executable software under GPLv3. Having done so, they must not try to charge you extra for the corresponding source code (eg, s6d); nor may they try to prevent you from using and/or redistributing it under GPLv3 (ss 4, 5c).
But just because they sold you a copy under GPLv3, and (at the same time, or upon your later request) gave you the source, that does not mean they are obliged also to give your friend Bob a copy of either the source or the binary. You may give Bob a copy of the binaries, source, or both, and if you do that you must honour the requirements of GPLv3 when you do it; but neither you nor they are obliged to do so.
If a distributor charges too much money for a copy of the software, potential users may club together to buy a single copy, which they then all lawfully share, and usually it makes its way out into the wider world. Thus in practice, charging for binary access to GPL software generally only works as a business method if there is some considerable value-add. But it's perfectly acceptable to do it.
Also: the above argument only applies if the distributor is obliged to follow the GPLv3 with respect to this program by having acquired it under those terms, or having incorporated someone else's GPLv3 software into it while making it. If the distributor is the sole rightsholder1, (s)he may offer it under multiple different licences. (S)he may also offer different versions under different licences; when this happens, it's common for the non-freely-licensed version to be somewhat whizzier and slicker (the Open-Core model).
I can't find anything (yet) that confirms that Helyx is a derivative of OpenFOAM, but if it is, it may well be that it's the whizzy version of OpenFOAM, offered under less-free terms as described above; or it may well be distributed under GPLv3, but only to paying customers, also as described above. Only Helyx can tell us what's going on, and I'm not asking them.
So to answer your initial question: the rights granted by FLOSS (as per the FSF, OSI definitions) are a pure superset of those granted by open access (however that is defined). But the question is, open to whom?
1 or has permission to do this via, eg, an appropriate CLA covering all external contributions.
