The usage of sandboxing in the Chrome cartoon seems very closely in line with how it has been used by operating systems and programming languages in the past, at least to me.
When I first learned Java almost ten years ago, one of the first concepts that was introduced was the "sandbox" - the idea that a Java app or applet is executed in a segregated section of memory so that if that applet or application attempted something malicious, it would not have access to anything else on the system.
The
SEO definition is a bit different, but it still refers to the concept of keeping things separate. In this case, a web site is in the "sandbox" - a waiting area before it is trusted and allowed to mingle with the rest of the sites in the index (whether such a place exists or not is a bit beside the point here).