That seems to be their M.O. when it comes to firing people now. According to their former lead animator, Shane Newville, they did exactly the same thing to him around a year after the death of Monty Oum, when they called him into work, had "the one guy he still trusted" (his words - I think he's likely referring to either Blaine Gibson or Barbara Dunkleman, but that's pure conjecture) ask him for his laptop in order to do "maintenance," and then immediately fired him once the files for all his work had been removed from the computer.
Here's an archived version of the Google Doc - the company vehemently denies everything detailed in the document, but Kathleen Zulech (who voiced Tex in Red VS Blue) and Monty's wife Sheena asserted that it was all true.
While people seem wary of Sheena's intentions, I feel like Kathleen has no reason to lie in Shane's favor, since she was an independent contractor and hadn't been working for RT in years by that point. So hearing that they did the same thing to Joel that they did to Shane years earlier comes as no surprise to me.