Your classmate is either engaging in a rather pointless exercise of historical hairsplitting or peddling some variation of a common trope that circulates among Holocaust denialists. As a historical process, the Holocaust was not one single discrete event, but rather a series of interconnected ones. Expropriation of property, ghettoization, and violence (organized and casual), worked to mutually reinforce each other. In this situation, Hitler not only authorized the these actions by delegating to his subordinates, he served as the genesis of these various actions.

In this case for the earliest atrocities, that would evolve the activities of the Einsatzgruppen in Poland in 1939/40, with the first mass shootings occurring in September 1939. On 18 September, members of the Waffen-SS unit Leibstandarte Adolf Hitler executed fifty Jewish prisoners. Although this formation was under the command of the 10th Army, its Heer commander von Reichenau did not give the order for the mass shooting, and contracted is superior for clarification, von Rundstedt who in turn telephoned Hitler directly. Hitler informed von Rundstedt that these actions fell under Himmler's responsibilities and not the military's. Hitler had authorized the SS to take command of issues of security and pacification in the wake of the German invasion, a task that the SS heads Himmler and Heydrich were quite willing to accomplish.

The Waffen-SS and Einsatzgruppen's mass shootings were a part of the larger process of eliminating any unwanted racial component of the formerly Polish land. In a 20 September meeting with OKH head Franz Halder, Hitler reiterated that resettlement of the areas directly annexed by the Reich would entail pushing out two Polish inhabitants for every one German settler and Jews would be forced into ghettos in the General Government. Hitler already had issued a blanket amnesty for crimes committed by military and SS personnel on 4 October and two days later declared to the Reichstag that the successful invasion of Poland had enabled "a new order of ethnographic relationships, that is, a resettlement of the nationalities." Soon after this declaration, Hitler sanctified the SS's growing control over the nationalities issue by appointing Himmler Reichskommissar für die Festigung deutschen Volkstums (Reich's Commissar for the Strengthening of Germandom). In records of various speeches and conferences, Hitler repeatedly called for the elimination of racial filth and displayed a callous indifference to the suffering that was the natural byproduct of these policies.

Whether or not Hitler "knew" the exact details of events on the ground is neither here nor there. Like many national heads of state, he delegated to subordinates to carry out his various initiatives. In this case, delegating the control over the population and resettlement of Poland to his most extreme racialist paladins, Himmler and the SS, he sent a clear signal that this violence was sanctioned at the very apex of the German government.