It's not noted in the article, but it may be important that Stentor is a ciliate (same group as paramecium). Ciliates are very elaborate single-celled organism

It's not noted in the article, but it may be important that Stentor is a ciliate (same group as paramecium). Ciliates are very elaborate single-celled organisms, with the unusual feature of having a "macronucleus" in addition to a "micronucleus" that is similar to the single nucleus of other eukaryote cells. The macronucleus contains numerous copies of DNA from the micronucleus, which could provide a lot of scope for states that are represented in terms of gene activations, allowing behaviours such as described in the article.