There are a lot of claims without any evidence in that blog post. "The RNA in a cell is the only entity which is active and carries significant bit density." is one of them.

DNA certainly encodes for a significant amount of information as well. And why not proteins, there are a lot of proteins in a cell and you can also modify them in various ways. A cell has an enormous amount of state, any of it could theoretically store information like memory. There are a lot of different molecules active in a cell, in various modification states, at various locations, and all of that could encode information.

What this blog posts doesn't provide is any experimental evidence, this is a pure thought experiment. If RNA were to actually store memory, that would be great. Because determining the RNA sequences inside a cell is something we can do.