By “fluidity of the digital” I think Ritchin is talking about the constant changes that the digital landscape is seeing. Throughout the years the role that the digital plays in our daily life is constantly changing, for example 5 years ago nobody knew what and NFT was and very few people knew what a cryptocurrency was. However, now you cant go 5 minutes on social media without reading something about NFT’s or cryptocurrency. This could also be in reference to the manipulation of digital media and assets. This is becoming more of a problem that people are talking about, for example the discussion around fake news, and the misinterpretation of data. While these have always been problems, but now that these misleading articles can be so easily accessed and shared around the world it makes it harder to find what is true and what is false. Now with the boom in crypto currency there are a ton of pump and dump scams, that get people to invest before the creators of the coin sell everything at when the price is high and leave everybody who invested to take the losses.
Such as photography captures real life the digital media captures peoples imagination. For example on youtube there a millions of creators that upload their content, and many of these are capturing peoples ideologies and there imagination. The creative freedom that digital tools give us access to helps people manipulate things to better express how they imagine things and what they imagine them to be. So if photography captures reality then digital captures what we imagine reality should be.