3 primate species where very concise tests showed that they were close to or occasionally slightly better than humans in specifically rigged short term memory tests (after being trained and put up against humans going in blind).
I've never heard of any test showing an animal to be significantly more intelligent than humans in any measure that we have come up with to measure intelligence by.
That being said, I believe it is possible that some animals are either close enough to us that they deserve to be called sentient, and I believe it is possible that other creatures on this planet have levels of intelligence in specialized areas that humans can never hope to approach unaided by tools, but as far as broad range intelligence, I think we're this planets' possibly undeserved leaders.
I don't think working memory has much at all to do with sentience.
The conversation was more about long-term memory, which has not been sufficiently studied in animals (nor am I certain it can be effectively studied at all).
Even then I don't think there is a clear relationship between long-term memory and sentience either.
