This is accurate. It is slave labor because corporations go out of their way to harm the developers of open source projects which they benefit from because they

This is accurate. It is slave labor because corporations go out of their way to harm the developers of open source projects which they benefit from because they view them as competition. They engage in blatant anti-competitive practices while benefiting from their victim's work. It's slave exploitation as evidenced by the lack of payment for labor which, from the perspective of the open source developer, was motivated by the complete deprivation of opportunities for paid labor. Many people make their project open source because they know that their project would have 0 chance of getting any adoption unless they gave it away for free. The masters created market conditions which deprived the slaves of any opportunity for fair remuneration (made possible by the design of the modern monetary system).