Okay so, my sock wanted a manga version of this feat, since this used the anime where the explosion isn't portrayed to be nearly as big. Also I'm told that the meteor might be 200 meters in height as opposed to diameter like the calc used, so overall, something should be done here.
In case of it being height instead of diameter, the meteor in this shot where it doesn't seem all that destroyed enough to inflate results is 642 pixels wide and 938 pixels tall, making for a discrepancy of 0.68443496801, making the meteor 136.886993603 meters in diameter
(Ignore the 200 meters part, I didn't make the image, I just used it because it was convenient)
The meteor is 20 pixels wide, while the blast is 650 pixels, a discrepancy of 32.5, making the blast 4448.8272921 and 6500 meters for low and high end
Using near total fatalities considering the blast is off the ground, ((4.4488272921/.28)^3)/2 and ((6.5/.28)^3)/2 makes for...
Low End: 2005.54563851 Kilotons, 2.00554563851 Megatons, Small City level
High End: 6255.12481778 Kilotons, 6.25512481778 Megatons, Small City level+
Dunno how much perspective screws with the blast itself, that's up to discussion.