It depends on which license.
There are some free software licenses that are specifically designed to prevent people from doing stuff like that, such as the GNU GPL. They're known as "viral" licenses, because their licensing terms spread to any code you use them with, which keeps you from using a GPL library in a non-GPL (or compatible) program.
Other licenses are more concerned with freely sharing code than with pushing a particular ideology. Somewhere in the middle of the spectrum, you have the MPL (Mozilla Public License,) which is non-viral and can be used in proprietary projects, but the license terms require that the MPL code itself remain covered by the MPL, and that any modifications (such as improvements, bugfixes, ports, etc) that you make to the MPL code must be published freely. The idea here is "you get this code freely, so if you improve it, you should contribute your improvements back to the community as payment."
And at the far end of the spectrum are the completely open licenses, such as the BSD, MIT and Zlib licenses. They essentially say "this code is free for anyone to use however they want." (With a few restrictions, of course, but there's really not much to them.) People using these licenses are making free use of their code the highest priority.
So not all free software licenses are created equal. Take a look at the licenses that are being used here, and what their terms are, and you'll get a better idea of whether or not the developer is complying with them by using them in a proprietary project.
Also, there's a fourth possibility: The "fairly large company" could have licensed the product under different terms. A software license is designed to limit users of the software, not the creator of the software, and it's not unheard of for someone to release an open-source library under GPL-style terms, and then also sell commercial licenses for it to people who want to use it in a proprietary project, without their codebase being "infected" by a viral license.