169.254.x.x is APIPA,windows will auto-assign a random address in this range when it connects to a network and doesn't have a static address assigned AND doesn't receive a DHCP offer from the network it attached to, as to why you connected to the AP in question, what was the SSID, if you had associated to an open AP that had a default SSID and then came across another open AP at the new location with the same default SSID not much mystery there. What was the SSID you auto-connected to?