Whenever that quote is made it is always ripped from its context. By the time of Goldin's interview, missions beyond Earth orbit were planned that included long term lunar missions, trips to Mars and so on. All missions that would last far longer than Apollo. In terms of radiation exposure, duration is a key factor. Rather like walking to the corner shop in a light shower and getting a little damp, or doing a 10 mile hike in the same light rain and getting soaked through to the skin, a short trip of a few days in the radiation beyond the van Allen belt is harmless, but several months out there may be lethal.