No, other way around. The patch which decreases Intel performance has already occurred. This patch AMD saying "we don't need this, so we're disabling it for AMD CPUs."

Because of the rest of the patch set. This one simply says "AMD CPUs should not be penalized [by such patch set changes]".

There's code going in to perform some extra work to workaround some CPU bugs. This disables that work on AMD, because the bugs are not present there. Intel will have to do the extra work still as the bugs are present in Intel CPUs.

The full details are as yet undisclosed, implying there are security issues arising from these bugs (also the name of the flag)