Here is the actual quote from John Linneman:
I don't fully understand what "high-end demo hardware from a partner" means, but what I'm forced to take away from this quote is: John believes Nintendo may have shown a demo (in private, to selected developers) which is not actually representative of the power of the hardware it was supposed to be demonstrating the target specs for. His reason for believing this is "battery life," which -- if we're generous and extrapolate for him to include heat dissipation and the like so it actually applies to docked mode, which is the target spec that would have been shown at Gamescom during a 4K BotW demo and the like -- suggests that Nintendo put together a demo for a higher target spec than the one they will ultimately clock the hardware for.
But... they're the ones who made the demo. To show off their own hardware. With the comparison to the TX1 not maxing its rated clock on the Switch, it almost sounds like he thinks the demo was made by Nvidia based on T239 running at its max rated clocks, with no consideration given to the Nintendo hardware it was actually going to be used in, but that's obviously not true. This isn't Nvidia demoing T239. It's Nintendo demoing their hardware.
I find this bafflingly dumb. The correct thing to say regarding the demos -- which has been said here many times already -- is that we don't actually know firsthand how they ran, or how it would stack up in practice to other consoles, or really anything beyond the fact that it sounded encouraging and certain technologies (ray tracing, fast loading) were present. No one reacted to the news of those demos by thinking we're getting a portable PS5. Going all the way overboard in the opposite direction, and saying that the demos don't necessarily have any relation to the hardware's performance, comes across as woefully uninformed contrarianism. It's not like this is a cleaned up promotional screenshot on Twitter! It was a target spec briefing for developers that Nintendo wants to make games for their hardware! I can't wrap my head around this take at all.