As usual Linus is talking 'general' but thinking focused.
What he is actually talking about is high level computers (which these days includes smartphones, tablets, etc however there is a little
more crossover there).
Where he has no knowledge, understanding, or consideration is lower level applications - ie :embedded.
Arms flexibility, and tendency to closely integrate hardware at the low level makes it is fantastic micro CONTROLLER implementation in general.
The STM32 series are a great example of this, and it is an area that Intel seems to have lost the plot on. Despite Intels gushing money from time
to time into such areas, very very few would touch them with a barge pole. Their IO infrastructure is just TOO complex and unnecessary for such
applications (no one there uses PCIe, etc. Even USB tends to emulate a serial device).
In the mid range - ie: cellphone, tablet, etc ARM Chip sellers integration is great, however their documentation is TERRIBLE, and they do not seem to understand that open hardware specifications are gold (I am looking at you allwinner, rockchip, amlogic, himedia, mediatek, etal) and who dont seem to realise that sharing that knowledge gets a LOT more developers on side (or possibly hide it because of IP fears... who can be sure). There are vendors without
such problems however (generally but not exclusively the non-chinese chip makers).
In the high end - PCs, Servers, etc. well, thats a mess right now. Perhaps AMD etc will help sort it out, or perhaps not.
In the end, ARM makes sense in a whole lot of niches, however not really those Linux focuses on - his primary focus has always been large server and workstation hardware, an area ARM is only just starting to overlap into in a small way.
So, what he says is factual in one area, but that area is a niche to arm, and a stronghold of Intel, so is it really a surprise?