Can anyone identify this type of green tea?
In general, your description - dark green balls which unroll to full tea leaves, sounds like some variety of gunpowder green tea.  It is a quite common Chinese technique, as I recall.  Each pellet (also sometimes called "pearls") is a rolled and dried tea leaf, which unfurls when steeped. 

However, it is difficult to get more specific than that without more information.  There are several types of green tea that can be rolled into "gunpowder" form, with differing grades of tea, amount of aging, and years or growing locations (given growing conditions) all contributing to somewhat different flavor profiles.  You might be able to use the terms and look to see how the information about which varieties of gunpowder green match your house mate's tea or your experiences (or your own preferences) - but without more knowledge I don't know how to pin down the same kind of tea.