The match could not be through the male match's MtDNA since he could have only gotten it through his direct maternal line. His maternal great grandfather would have MtDNA from his own mother but, as a male, couldn't pass it down.
Like the other responder explained, in most cases the usable results from MtDNA testing is very limited in terms of being able to confirm a common ancestor. I did the Full Genomic Sequence testing on FTDNA and have pages of matches but have found no definite common ancestors, although in two cases we had ancestors in the same geographic areas and so can reasonably infer a common ancestor within a generation or two of our earliest known maternal ancestors, just not a definite individual. My ancestors were here in Colonial times but many of my matches are with people whose families have never left Europe or Canada.