It's not a surprise, although not for the reasons you mention. We've known about similar deposits in permanently shadowed craters on the Moon, and one of Messen

It's not a surprise, although not for the reasons you mention. We've known about similar deposits in permanently shadowed craters on the Moon, and one of Messenger's early discoveries was of craters with similar conditions on Mercury. However the source of the volatiles is not the type of chemistry that happened on early Earth, but rather cometary deposits and exospheric interactions.