It's going to be unclear what exactly happened for quite some time, and a precise magnitude measurement may actually take months.
I've seen this happen with other quakes on FR.
People are under the impression there's ONE magnitude scale and that a few seconds after an earthquake there's one simple accurate measurement and that's the magnitude.
There are actually SEVERAL different magnitude scales, some are more accurate or less accurate based on the size of the quake, and quakes will typically be a different magnitude on each scale.
What you see on the internet quickly after a quake is an AUTOMATED solution by a computer connected to a seismic network; these often are quite wrong, will report one quake as several quakes or several quakes as one quake, get the magnitude and/or location wrong, etc. Compounded when you don't have a dense seismometer network..and the Midwest doesn't have the network California does, though the immediate New Madrid area does.
So you'll see magnitudes of quakes constantly changing as humans review the data, etc. One problem the media has in big third world quakes is immediately using the number provided by the local country which often is far too low, and they never revise the number.
Damn. A 5.0 is a lot more potentially dangerous than people think, outside of areas with hardcore earthquake-proof-building regulations like SF and LA. In Manhattan, a 5.0 could cause some very serious damage and a lot of deaths because so many of the buildings are unreinforced brick masonry. The skyscrapers would be okay, but your brownstone wouldn't be very pleasant afterwards.
(And just to give Manhattanites a little something extra to worry about, there are actually major fault lines running right under Union Square and 125th St. The Big One will hit NYC one day, too, just like in SF and LA. Except we're not the least bit prepared in NY.)