Airbnb apartments are tending towards the "hotel room" look because that's what most of them essentially are. However, every Airbnb I've been in over the past few years has not looked anything like that, so I suspect some bias from places the author goes.
Interior spaces most definitely don't look the same. I think this is just the author extrapolating from their Airbnb experiences. The middle class homes will definitely look similar because they all use the same source material (same as they always have - just websites now instead of interior decorator magazines).
Consumer brands are all over the map, just like they've always been. And it's not like we haven't had bland brands like General Mills and Polo and Sears for ages.
Apps and websites follow the trends because that's what you do in the media space. Nothing new there.