Cuba being not removed may have been for that reason, but Cuba being placed on that reason was not for that reason. While one might argue that the terrorism involved was no different than what the US and US-allies backed on the other side of the same global conflict, when Cuba was placed on that list it was actively backing terrorists around the world as one of the most active nations, behind the USSR itself, globally promoting the Soviet-led Communist movement. (If you look at the list in general, the pattern of countries being added for real reasons, having those reasons largely go away but remaining on the list until some agreement not directly related to any supposed active involvement with terrorism between the US and that country is not unique to Cuba.)