They got the origin wrong: 'van' is of Dutch origin.
Many Dutch surnames have prepositions such as 'van', 'van de', 'van der', etc. Capitalization rules in Dutch for these names are pretty complex. If there are two prepositions in one name (e.g. 'van der') the second word is never capitalized. The first word is not capitalized if another part of the name (first name, initials, spouse's name) is in front of it. Otherwise it is capitalized. The 'real' surname is always capitalized and also determines the place of the name in alphabetical order. Some correct examples:
Jan van den Berg
Mr. Van den Berg
Mr. J. van den Berg
And suppose this guy's wife was born 'ten Haaf', her name would spelled as:
Anna van den Berg-ten Haaf
Both Mr and Mrs van den Berg would expect to find their name under 'B' in the phonebook.
Please note, all this is just the simplified version of the capitalization rules
