These are not something to be nibbled with tea, but they are tea itself. Green tea seedpods, to be exact. Rough to the touch and nearly light as a feather, they rattled a bit as I rolled them about in my hand. Sankyoen-san patiently explained to me in the simplest Japanese he could muster what they were and how to plant them. They have since sat in a small bowl on my bookcase waiting for me to make my move.
While Sankyoen-san's advice is certainly sound (as the twelfth generation of his family to grow tea, I assume his knowledge is near encyclopedic), I also did a bit of research on my own to find more details than my limited language skills and his busy market table would allow. The general consensus seems to be that the seeds need to be kept moist and planted fairly quickly in order to remain viable. (Mine have not had the advantage of either of these things, so I'm a little concerned.) Some sources recommend scarification of the seeds, and other simply recommend soaking until the seeds crack. If the seeds float, they are not viable at all and should be composted. (Mine are floating just now, but I'm hopeful they'll sink. If that means they are still viable, I don't know.)
Despite learning yesterday that my hopes of home tea growing are sunk (the seed pods did not sink or crack or anything), I did manage to find the following links that were incredibly useful for growing from seed or cuttings.
Easily the best resource comes from The Field Alliance (formerly known as the Community IPM Programme), an organization working to keep farming a viable economic alternative in rural communities in Southeast Asia. Their Tea Eco-Guide gives detailed information on growing from seeds or cuttings as well as soil preparation. Arguably, it is more than the home patio grower needs, but it makes good reading and satisfied my desire for solid information.
The University of Florida Extension Service offered good information for the home grower as did Narien Tea Store. (I don't usually reference company sites, but their information about growing was some of the best I found.)