Is he an engineer or scientist type?
If someone said to me that they were "aromantic" (without looking up defenitions) I would take that to mean that the things the media puts out as being romantic just don't do it for them. The flowers, cards, gifts, poetry, long walks on the beach, etc.
I identify this way most of the time. My idea of a romanitc weekend is going backpacking with just the two of us, not some fancy hotel with a bunch of spa treatments. All the fancy "romantic" sentiments really weird me out sometimes.