I have several comments about this.
1st of all -
watch this 24-in-one apartment in Hong Kong. It's way more impressive, although it's also much bigger relatively speaking (330ish sq. feet).
2nd of all - she's clearly acquired this as a bit of a calling card for her organization business. This woman can honestly say she fits her life into 90 square feet. As an "organizational consultant" that's gotta be gold.
3rd - if you live in a big city (a really big city) then this isn't that shocking, although almost no one would still bite. They'd rather just move further out of the high density areas. But as (very few!) have pointed out, there are those city dwellers - I've had several as friends - who are out all the time. They literally need a meatlocker to store their body for sleep and a few possessions. In fact I'd say this type of hyper-mobility is become more common, not less (see:
neo-minimalism). If you have the sort of lifestyle where you simply are afforded amazing access to some world-class services (i.e. downtown Manhattan with no commute) then you can easily get by. You just need mail and a secure drop for your stuff, really. Ate out all the time, spent spare time in coffee shops or what have you. No car payments, no travel time to speak of. Hell one of the guys I knew had so much extra cash he would just get a nice hotel room when he hooked up. He had that because he had a tiny place that he didn't really care about.
It's not for everybody (or me) but there's definitely something to living this way, it has an amazing appeal if you really are a city person. I imagine most suburban/rural dwellers would look at this article and think the size was pretty crazy, without context.
Plus on a personal note, I find something really cool about the kind of "forced optimization"; this high density living can sometimes make humans use resources and behave better in certain ways, just because they are much more motivated to.