a traceroute shows the outbound route. it's possible for the the probe packets to follow one path and the returning icmp packets to take another path. a looking glass in the AS your tracing to is a good way to see what the return path is...

The returning ICMP packets may take many different paths back to the sender of the UDPs, since each hop will make it's own decision on how to return to the source (not just the single asymmetric path from the destination of the UDPs). Kris