There's around one mutation each time it transmits between hosts (for flu it is one each time it goes cell to cell). 1,136 doesn't seem that high, say it hops 100 bats a year, that's just a divergence of 11 years of bat hopping (the more mutations that add up maybe the rate doesn't hold due to conserved regions though?). 5X less hops a year, 55 years: still a blink.