Obviously this wasn't always the case, e.g. a good 15+ years ago I put ucLinux on an old ISP router I had lying around for fun, and it was an ARM946 without an MMU. But that class of device no longer exists today for all practical purposes, and so it's easy to use the existence of an MMU to decide what to call them.
The 8086 may have been a microprocessor, and so was the 80186, but you know where you find 80186 cores today? Microcontrollers. Specifically, some video processing chip manufacturers (e.g. stuff that goes into monitors and DP-HDMI adapters) seem to like using V186 cores still.
The problem with these definitions is a control device and computer are two different things, so I wonder if he is applying an engineer's perspective/definition to the 8086 even though many know the 8086 were used in the early computers. This is a bit like arguing whether a microprocessor is a microprocessor because of the inclusion or exclusion of one or more instruction sets, ie a basic intel cpu with a minimum instruction set or a xeon intel cpu with a much more extensive number of instruction sets.
Or are you picking up on an AI masquerading as a blogger and have highlighted something an AI wouldnt pick up on from online technical resources?
We know definitions change over time because slang words come and go and someone's vocabulary can be used to identify people online or identify their knowledge.