The style of Keith Caves reminds me a lot of the style popularized by the Underground Comix movement very popular in the late 60's and early 70's. This style can still be seen in mainstream publications such as "Mad Magazine".
It is hard to pinpoint this style to that particular illustration, so I am basing my answer in the rest of the examples of the artist's work shown in the page you have linked.
The style very often used iconic imagery from early comics (like the runaway inmate with its striped uniform) but subverted it with "shocking" and taboo themes such as sex and drugs. They were usually parodic in nature and loaded with social criticism.
Other examples of the style had a more rendered and overly graphical style with a full and open intention of being grotesque, like some of the examples of the artist's work.