future perfect (will) for past events

She will not have minded much when Kenneth Clarke, a Tory grandee who is a former home secretary as well as chancellor, was picked up on a microphone this week calling her a “bloody difficult woman”.

[Source: Economist.com]

I understand it basically means that she did not mind it. But why should "will not have minded" be used which as far as I know is future perfect?

Like most modals, "will" has an epistemic meaning as well as its principal one: a meaning which as about the speaker's knowledge rather than about how the world is.

The epistemic meaning of "will" is something like "I conclude", so the given sentence means something like "We presume she didn't mind when... "

The OED, s.v. will, v., meaning 15 d.: " With the notion of futurity obscured or lost: = will prove or turn out to, will be found on inquiry to; may be supposed to, presumably does. "