This is a great example of why both sides of a story are needed. From DEF CON's perspective, assuming this is all true, there's nothing unreasonable here. It sounds like Dmitry was a subcontractor of Entropic and producing a screen asking for money after their contract had been terminated (for good-sounding reasons) was bad form.
I'm not commenting on the legalities (I don't know anything about contract law) and I don't necessarily take either side's account at face value, but this response doesn't sound unreasonable to me.
If we believe the firmware's author that it was volunteer work, who was relying on him? Entropic or Defcon?
Did Entropic promise to deliver the firmware?
And assuming Entropic did promise a firmware, would the "stop work" order also affect firmware? Apparently the "easter egg" was added after that order.
> The specifics of what they requested in January were extremely difficult / almost impossible, but we had been working with Raspberry Pi as a Design Partner and had early access to the unreleased Raspberry Pi RP 2350, a chip that would enable exactly the kind of device DEFCON was requesting. Dmitry and Entropic had already been working on a GB emulator and were thrilled to be able to contribute our work to a project directly for and by the community.
...
> Despite the near impossibly short timeline to achieve 30k unit mass production, our team of 5 worked tirelessly alongside Dmitry. He handled all of the emulator software while we sourced components, designed all of the hardware, wrote production test software, and organized all circuit board manufacturing, prototype manufacturing, facilitated large volume production manufacturing and logistics, and general project coordination. Through this period, Defcon’s responsibility was the game-specific software, badge accessories (i.e.: plastic case and lanyard), and the printed circuit board artwork including the cat shape, colors, and silkscreen.
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It appears that Defcon contracted with Entropic. Entropic was working with Dmitry.
Dmitry didn't ask for money. He raised awareness that DEFCON had slinked away from its financial obligation to Entropic, and asked that Entropic be paid what they are owed for their work on the hardware.
I'm not commenting on the legalities (I don't know anything about contract law) and I don't necessarily take either side's account at face value, but this response doesn't sound unreasonable to me.