I should start this answer by mentioning that it's almost impossible to truly trace a community transmitted viral infection with 100% accuracy, which would make it difficult for any plaintiff to prove their case.
I could also point out that any judge (at least in the United States) that is presented with such a customer infection case would likely dismiss them outright except for instances of gross negligence, since at this point anyone who goes out in public knows the risks of contracting COVID-19.
But alas, I am not a lawyer. And while there are plenty of lawyers working for the industry trade groups we queried over the past several days to get an answer to this question, none really had a specific answer.
Apparently, the cinema industry is not alone in trying to answer this question... so is everyone operating any form of business, as is evidenced by this recent article in The New York Times: