Anger aside, he's right. mesa is used even if the intel driver is used too. mesa includes a software implementation, but it's also the gateway to the hardware drivers.
Better stated: the Intel graphics driver is part of the Mesa/DRI2 framework. Mesa's core provides the OpenGL front end (API implementation, shader compilers, high level optimizers). Intel provides a low level component that takes that shader stream and turns it into programs and commands for the hardware, which is managed by a DRI driver in the kernel.
