Bernie has been opposing U.S. adventurist military interventions for his entire career. It constitutes an unbroken consistent stance over multiple decades and multiple U.S. Administrations. Those comments of his from the 80's were made within the context of Reagan's thinly veiled clandestine military support for the Contras in Nicaragua. Bernie had a point to make, and it was as important then as it is now. It is that the U.S., through a combination of military might and wishful thinking, can not impose regimes to our liking on the people of other nations.
The example he used regarding Castro, and he used it in his full interview, was that it was arrogant and foolish to have believed that the entire Cuban people were going to rise up and overthrow Castro when the Bay of Pigs invasion occurred. They didn't, and it is as important to recognize the reasons for that failed military policy objective then as it is to recognize the failure of the U.S. military policy objective behind Bush/Cheney's invasion of Iraq. Cheney, in particular, promised that a U.S. invasion of Iraq would be a short lived cake walk, with the mass of Iraq's citizens waving American flags and cheering us on as "Liberators". They didn't. Just like the people of Nicaragua did not openly embrace the Contra forces as their liberators either and quickly overthrow the Sandinistas, just because Reagan wanted them to.
Circumstances throughout much of the world where people are not free to Democratically choose their own governments are complex. Castro may have been brutal, but he overthrew an at least equally brutal right wing dictator in Batista. Ortega's government was no ideal bastion of democracy and civil rights, but he overthrew a brutal right wing dictator in Somoza. Many people suffered horribly under Castro, and many people suffered horribly under Batista before him. When true freedom is not an option many people chose to support one of their lesser options, which of two sides is more likely to ensure that their own families are fed, educated and housed?
America has zilch credibility for supporting the democratic aspirations of the people of other nations around the world. We helped overthrow a democratically elected government in Guatemala which has been followed by decades of chaos. We backed a coup that overthrew the democratically elected government of Iran and subsequently helped install the Shah, which led us down a road of conflict that continues today. We supported the overthrow of a democratically elected government in Chile, which led to the horror of the tens of thousands of "disappeared".And you know what I left out of the listing above? The U.S. military intervention in Vietnam. Over 58,000 American lives lost trying to save the Vietnamese "from Communism". We inserted half a million troops into a Civil War, and lost.
Even today, Trump has wet dreams of "regime change in Iran" as we hover on the knife's edge of military conflict with that nation. We need to recognize that given no viable "good choice", and unfortunately that is true for the people in dozens of nations around the world today, they will give their support instead to the perceived "lesser evil" choice, the one that will give them at least the greatest degree of basic economic survival assurance. Sometimes that will be a right wing dictator. Sometimes that will be a left wing dictator. But it usually isn't whoever Washington DC wants to install for them through direct or indirect military means. Our track record is pretty damn poor in that regard. THAT is the point that Sanders has to make. He was right then, and he is right now