His explanation assumed that immigration inspectors in 1961 either didn’t know or didn’t enforce U.S. immigration laws. I don’t find either hypothesis likely, though of course I can’t say for sure.
Obviously you never travelled between Canada and the U.S. in the 1960’s. Quite a few Freepers have relayed their personal experiences of travel between the two countries back then, including myself. When stopped at a border crossing in the 1960’s the driver of the vehicle would be asked for their driver’s license, but no passengers were EVER asked for identification, they were given a cursory glance at most before being waved on. Remember the border between Canada and the U.S. was often referred to as “the longest undefended border in the world” and this was definitely noticeable in the 1960’s!