In case you don't know the lead-up to this scene: a German aviator just out-gunned several bandits in the cantina for making fun of his clothes. The German informed the survivors that some friends of his are coming, and they are even less good-natured than he is, so anyone who wants to remain alive had best show them some respect. That's the German walking away at the 0:00 mark.
The German's friends arrive only after the Three Amigos leave, with hilarious blood-soaked results.