The empty 30ft (9m) cargo crashed through trees and a wall on an embankment near Scout Green, Cumbria.
No-one was injured but the Rail Accident Investigation Branch (RAIB) said the potential for more serious consequences was evident.
There were 62mph (99km/h) cross winds when the container fell on on 7 March, investigators said.
The authority said preliminary investigations suggested an ineffective spigot had been used to fix the container to the wagon deck.
But, it said, the freight operator had tried to minimise the risk of a container coming loose.
After the incident the operator reduced its guidance speed in high winds and issued a national incident report to inform the rest of the railway industry, the RAIB said.
The investigation into the incident is ongoing.
High winds blew a container off a freight train travelling at 75mph (120km/h), investigators have said.