TLDR: I went through the whole story, from Hitler joining the German Worker's Party, to becoming chancellor and tried to be as factual as possible, regarding the events. I steered away (and disproved where possible) the "great man" theory regarding Hitler. I emphasized giving context regarding the social, economic and political situation at the time, the prevalent ideological movements among the Germans, how WW1 and the Depression shaped German politics. I tried to show in a materialist way, why the Nazis developed the beliefs they held and why many other Germans were sympathetic to their message.

The original question was that he didn't know that Hitler was Austrian and how come an Austrian became Germany's chancellor. He then asked why the Germans were willing to follow him.

I explained that he was born in Austria but his family were ethnic Germans. Austria-Hungary was a melting pot of cultures, but the state at that time was dysfunctional, resulting in hatred between different population groups. Many Austrian Germans wanted to secede to Germany, viewing other cultures as holding back the rest of them. Hitler was exposed to this rhetoric throughout his early life, especially when he was studying art in Vienna.

I then went through the economic and political effects of the aftermath of WW1 in Germany, and the stab-in-the-back myth ("the German army was going to win, but Marxist and Jew politicians capitulated before that happened"). I find that explaining this myth, is the easiest way for people to understand both how Germans were willing to follow Hitler, and how fragile German politics were becoming before his rise to power. Although, if you use this, you should probably state that it wasn't the only reason.

I explained how Hitler joined the German Worker's Party (precursor to the Nazi party), which by that point had already embraced anticommunism and antisemitism, which appealed to him. However, this kind of rhetoric was already prevalent in Germany, following decades of cultivation of German nationalism and jingoism, the Spartakist uprising, and the stab-in-the-back myth being used widely by the right-wing opposition parties.

I talked about the Munich coup, and how the goverment, especially the military, were sympathetic to it, and how the Nazis escaped with easy penalties.

I then explained how corporations and other nationalist entities supported and financed Hitler and the Nazis, as a way to bust unions, dismantle the worker movement, and to stop (violently) the communists from attaining power. His oratory skills and his actions at the coup quickly gained him supporters everywhere, but especially soin Bavaria and Saxony, which led to the Nazis joining the parliament.

We talked a bit about the Nazi paramilitary thugs and how they were used to suppress worker strikes or outright assassinate leftist figures. I also emphasized how the Nazis, by their own admission, were using leftist iconography and anti-capitalist rhetoric to attract workers to their cause, but that they hardly believed much of it. They also gained a lot of popular support by targeting with propaganda, and aiding financially, people in areas most hit by the depression. Especially farmers and war veterans.

Finally, I explained that following the 1929 referendum to annul the Versaille treaty, organized by Nazis and their allies, gave them a lot of support, which weakened the other traditional parties at the next elections. Chancellor Bruhning started ruling by decrees, to deal with the financial crisis, since the parliament basically could not pass anything. Following this breakdown of politics, and taking advantage of the massive financial and political support that the Nazis enjoyed from the capitalist class, Hindenburg was pressured to hand the chancellorship to Hitler.

Wherever possible, I tried to establish how the capitalist class was very much linked to the Nazi rise to power.