I don't see it as a sign of anything more than the times. Not an anomaly but also not indicative of the state of the market. Even today, if you asked me, "Is there a market for 2,000 SF three-bedroom homes in downtown Boston," I'd say, "Yes."
You can't find a comparable property of the same size for the same price. The only difference is, the Bryant is in "no-man's land" between South End and Back Bay. But, compare it to 285 Columbus, just half a block down the street - they were able to sell 60+ units in less than 2 years. Some would say 285 Columbus is WORSE being that it is up against (over?) a subway & Amtrak rail line (and now has CVS as its anchor tenant - great place to pick up your Antabuse).
A fair question is, what kinds of buyers have the resources to close on these deals? Less than 50% sold means no traditional financing. The buyers aren't "rich" in the sense they don't have money to burn. Hope (and assume) they arranged their financing beforehand; don't know if they were able to get a mortgage contingency clause, I doubt it.
Would I buy in a building less than 50% sold? HELL NO.