Most people don't care about nominal difference in x86 vs arm. They care about cost, performance, efficiency, noise etc. Which applications run on the machine does matter.
The article never explained why the author wanted an ARM setup. I can only consider this a spiritual thing, just like how the author avoids Debian without providing any concrete explanations.
The usual reason to prefer ARM is efficiency, and the author's mention of replacing "power-hungry HPE towers" seeems to support that as a primary motivating factor.