I got the impression it meant a meeting for the intention of initiating a romantic (presexual) relationship. Like going to dinner alone together instead of with a group of friends.
They mention later that Japanese culture is more group-social than, presumably, the author's culture, and perhaps couples can have spent a lot of time together before calling it a date.
Aren't the Japanese big on "mixers" where you get equal numbers of guys and gals together for dinner/drinks - and a date would only be if you hit it off at one?
Of course there are other ways to get a date, but I suspect they have a pretty defined meaning for it.
The original whitepaper uses the term デート (transliteration of English "date") for the data, and I've understood the Japanese to consider that different from a mixer (合コン), and that a "date" is a one-on-one activity/outing with someone you're romantically interested in.
They mention later that Japanese culture is more group-social than, presumably, the author's culture, and perhaps couples can have spent a lot of time together before calling it a date.