What they talked about was kept secret until a 2009 interview where Gorbachev revealed that Reagan asked him ”
“What would you do if the United States were suddenly attacked by someone from outer space? Would you help us?”
“I said, ‘No doubt about it.'”
“He said, ‘We too.'”
While the casual agreement was never put to the test, one could speculate that it was simply Reagan’s way of putting things into perspective showing that at the end of the day, we’re all part of the human race.