It is true that millions died under the Nazis who were not Jews. They included targeted ethnic groups like Roma (Gypsies), homosexuals, left-wing dissidents, people with disabilities, etc. But it has long been a trope of Holocaust deniers and white nationalists to insist that Jews were only incidentally targeted.
In any case, there are no word limits in presidential statements. A more logical and worthwhile approach would be to note the various groups who were victimized. This isn't accidental. The new administration is riddled with anti-Semites and those who want to cater to anti-Semites.