It’s basically a (not very good) Farside rippoff (sorry!). The comic is a juxtaposition of two unrelated concepts with the idea that welding them together makes the joint idea ‘quirky’ and funny. Basically concept 1) people feed birds and 2) hippies dress a particular way, which ‘dehumanises’ them through the adoption of an ‘alternate cultural practices. As such, they all like hummus. It’s all stereotypes mashed together, really. Though, actually, ‘stereotypes mashed together’ is a pretty good description of a lot of ‘humour’.
To explain a little more, in the human mind all members of other groups are extremely exaggerated fictional copies of the ‘same person’. I.e., all French people carry baguettes everywhere and all hippies love hummus. As you can guess, these assumptions endure without actual truth.