While this is true, I think it is really arguing semantics. Whether it's a bug or a design flaw as you defined makes no difference. You could just as easily argue that a design flaw is just a bug in the architecture. The salient point is the same.I really don't think something is a bug if it's working as designed. A bug to me is an unintended flaw that affects performance, not a security "hole" that can be exploited in a product that works as designed.
The way I look at it is this: Bug = design was fine, execution had issues. In this case; execution was fine, design was 'flawed'.
If you really want to go down that route though, a bug implies that this was completely accidental. If you insist on calling it part of the design, you open it up for intel to be scrutinized over intentionally sacrificing security for performance as part of the design when their direct competitor using the same underlying architecture and principles got it right. Neither is good, the second one is probably worse though, imo.