Maine is well north of the Muscadine's accepted range, but have a look at the first link and compare your friend's vines with these. They are quite different from "normal" grapes (unless you are in the S.E.States in which case these are normal), and do require both male and female vines to produce fruit. (Also do a Google Image search for "muscadine").
For vines "gone wild" several problems with fruiting can occur. Grapes only fruit on the current year's growth, and with old unpruned vines, a lot of that can be out of reach and out of sight. Heavily vegitative growth can also leave little strength for fruiting, and also little "inclination"; the opposite of a stressed conifer putting out a huge crop of cones. Plants that are already successfully propagating themselves by layering (wherever these big old vines touch the ground and root) sometimes seem to know that they don't need to spend much effort in fruit production.
Assuming these are not Muscadines (but don't take my word for it!), pick a few of these vines that are favorably located - sun, drainage, away from frosty hollows - and prune them enthusiastically during this year's dormant period. I don't know when that is for Maine, but well after the leaves have dropped, but before they bud out in the spring. That should wake them up and you can see what you have.
MUSCADINE GRAPE Fruit Factsl
Pruning Grapes in Home Gardens
Grapes: Cultivars, Training and Pruning; G82-618-A
- scroll to "Neglected Vines"