"Dutch Bingo" is an in-joke.
Starting in the 1840's or so, groups of people from the Netherlands immigrated to the United States (particularly Holland, Michigan and Pella,Iowa.Basically, they had a doctrinal dispute with the official Reformed church of the Netherlands and decided that it would be better to try to make a life for themselves in the United States.
Their descendants started the Christian Reformed Church, the Protestant Reformed Church, the Netherlands Reformed Church, the Independent Reformed Alliance, the United Reformed Churches or became part of the Reformed Church in America. Because of this, memebers of any these denominations can usually find a common friend or relative within minutes.
If you note the large number of denominations versus the relatively small number of Dutch descended Americans, you might also note that they have a tendency to schism
In any case, a "Dutch Bingo" related conversation usually starts as follows "I went to (such and so) Christian Reformed/Reformed church/school/college in (insert city here)." The reply will usually be, "Oh, do you know (insert name here)?" And do you know what? They usually do.
Alternately, all you have to say is your last name and someone meeting you for the first time will turn out to know a large portion of your extended family.
Personally, I've met relatives this way.