As the TSE can be observed with the naked eye, the corona cannot be very bright. In fact the moon at this time, "by contrast", may be brighter than the corona.
"Appears to be black" Just what does this mean in plain English. The writer on Wiki obviously knows that the Moon is not black in reality, because it is lit by Earthshine, so chooses to make it "appear to be black by contrast," but gives no factual degree of illumination for either the Moon or corona. No evidence is given as to why or how this "black by contrast "could occur.
What we see IS BLACK. The Moon must be well illuminated. The black disk we see may not be the actual Moon.