There is another key aspect that separates true science from imposter pseudoscience. I could publish extensive research on how my cat is secretly telepathically communicating with extra terrestrials, but only when nobody is looking. But no amount of commentary from others in the feline psychic SETI field would make that research 'science'. What sets that absurd scenario apart from genuine science may be counterintuitive to people who don't understand science, which is why pseudoscience is so pervasive. Specifically, the one thing that sets real science apart from pseudoscience is falsifiability. Scientists actually want their theories to be proven false, and formulate them in such a way that it if they were false, it would be (relatively) easy to show it. In fact, the way scientists provide evidence for a theory when they publish it is to assume from the beginning that the theory is false (called the null hypothesis), and provide research which shows that it is statistically very unlikely for the null hypothesis to be true.
Rossi, on the other hand, starts with the premise that his device does work, doesn't entertain any alternative theories that would explain his results as would be required by a null hypothesis, and adamantly rejects anyone else's attempts to do the same. Therefore, his work is soundly in the realm of pseudoscience.