Did you really think she/he was suggesting that the US is setting up landmines in Vietnam 50 years after the war?
Landmines can kill people a very long time after being deployed you know...
Do you really think the US government bears no responsibility for the actions of the US government 50 years ago and the consequences today? Would you extend that to other governments too? In what circumstances would you not? What Cut off period do you think is right generally?
For example do you think the US has no responsibility towards Pacific Islanders whose islands are now lethally radioactive due to nuclear tests 50 years ago, and can reasonably wash its hands of any problems arising from that today?