Well, to be fair, he's right. 32-bit is only interesting in the embedded space. If you're running a "real" operating system, there is almost zero cost to running a 64-bit processor instead nowadays.
I'd go further than him, though. OpenBSD has limited resources. Those resources are better deployed on security enhancements which filter out to other operating systems that support less common architectures.
"Embedded" is too vague to use for this. Tons of STB's have SOC's with MIPS cores and Linux kernels (and uclibc). The cost could be the cost of the transistors used up by the CPU cores that could go to valuable functions like codec support. The cost could be RAM interface circuitry. The cost could be a dozen things and Linux is adopted in this category of system. It's almost like OpenBSD is defining itself as too good for use in economical, workaday products. I'm sure that would be a misunderstanding by me.
I'd go further than him, though. OpenBSD has limited resources. Those resources are better deployed on security enhancements which filter out to other operating systems that support less common architectures.