It's a play on a double meaning of the word "congested" (from Oxford Dictionaries):
1. (of a road or place) so crowded with traffic or people as to hinder or
prevent freedom of movement:
"the congested streets of the West End"
"the road was congested with refugees"
2. (of the respiratory tract) blocked with mucus so as to hinder
"his nose was congested"
It's also common to refer to the data transmitted on a computer network as "traffic," and hence refer to a network with insufficient capacity as "congested:"
2. The messages or signals transmitted through a communications network
"data traffic between remote workstations"
In this case, it's making a joke about Marshall (Wilensky), one of the authors, who we must assume has frequently-congested sinuses.