The company (Adjoint, Inc) is described as "digitises cash and settlement processes", something that cryptocurrencies aim to do as well. His company clearly doesn't use decentralization (since why would he make a post against it?), which cryptocurrencies do. How is that not a conflict of interest in this specific blogpost?

Reading the post it seems like he has no stake in the outcome of what people think about cryptocurrencies and decentralization, but that's not true, as a founder he has a huge stake in the outcome.

"Conflict of interest" here would require that he's in a position that gives him some special power over whether people continue to invest in crypto (or "decentralization" generally). Writing a blog post is something anyone can do. The fact that he's put a financial stake in his views doesn't make it unethical to express them the same way as everyone else.

It's not that he shouldn't express his views in a blog. The part that feels shifty here is that he's not disclosing his position in the space in his articles. I think most people are at least somewhat susceptible to "It is difficult to get a man to understand something, when his salary depends on his not understanding it." so a disclosure of interest is useful to frame thoughts on a topic.

I didn't know about any of this until @capableweb brought it up. It explains a lot more about this series of blog posts.

The repo/company you linked is about utilizing zero knowledge proofs which is literally the best we've got in regards to decentralization.

If anything, that gives him credentials to talk about it?

All you'd have to do to look at their website and see that they offer a product to banks, it has nothing to do with decentralization. http://adjoint.io/