It's part of their 'A Boy and His Tiger: A Tribute to Bill Watterson' exhibit, of which various other artists are also contributing. All funds raised will go towards the Cartoon Art Museum's programs and exhibitions -- when humans are allowed back into museums -- which is fine by me because they ran a Sam & Max exhibit in the past.
I don't really know much about Calvin and Hobbes except that one of them likes peeing on the backs of cars or something. It's more of an American thing, I think, quite unlike the true European culture that is Asterix or Tintin, but if our pal Steve is drawing then I'm reporting.
What's that? Sam & Max is American? Quiet in the back!