He minimised it by comparing the description of some limited measures to stop illegal migration into a country with one of the worst crimes in human history. The two aren’t comparable and to imply they are equivalent is to minimise one and exaggerate the other.
Yes, he said the language in the 1930s, not the actual holocaust, but the implication was clear. After all, the nazis aren’t regarded as one of the most evil regimes in history because of their language in the early part of their reign. It was clear the line of argument he was making was to equate the current actions of the government with those of Nazi germany. That is an absolutely risible comparison that is offensive and beyond contempt.