While yes, this does apply to PoC roles (too often do white actors voice PoC characters), it's not just that. If anything, PoC voice actors don't really get to do many roles beyond the PoC roles they do get. Granted, a lot of this falls more on the casting directors, but Stephanie is calling on VAs to do what they can on their end (barring NDAs getting in the way, of course). There has been some recent progress on this front, as newer black actors like Zeno Robinson have been getting roles like Hawks in My Hero Academia & Ross in Fire Emblem Heroes. But more can be done, & I hope that Stephanie's message doesn't fall on deaf ears.
Source: Stephanie Sheh (Twitter)