The people at OpenDNS gave me this explanation which I feel is the correct one: "Comcasts DHCP switch/router in your neighborhood/area had cached information that said all listened-traffic from a specific IP was to be directed to OpenDNS DNS servers unless specified by the user. This could happen because a user who had your IP before you had setup OpenDNS, and, when you inherited the IP, inherited the settings." So long as my lock is set on the TCP/IP panel, it should not happen again.