That's not really what it says. It's not even all that negative. It just raises some issues with the concept while curiously leaving out a couple of very important points.
First, this guy doesn't know what he's talking about:
"No one should think it’s cheaper than building a stadium; the requirements are the same for life safety, fireproofing, egress — everything has to work and be to code, meaning the way you build it is not going to be that much different from a permanent stadium,"
Yes, it is. The cost savings don't come from going skimpy on structural steel, the cost savings come from not including fancy suites, retractable roofs, and other luxury items that drive up the cost of American stadiums. The Patriots, for example, could probably build a permanent stadium for $500 million. Collegiate programs do this cheaply all the time - Baylor, for example, just built a $250M stadium that holds 45,000, and it's considered fairly top-of-the-line.
In addition to being sporting venues, your typical NFL stadium is also an office building and has a complex warren of team facilities, none of which would have to be replicated in a temporary facility.
None of this is to say that a temporary Olympic Stadium would be much less expensive than a bare-bones permanent one, but it will be far, far less expensive than the $1 billion the American public thinks of as a price floor for a "stadium" these days.
Second, whatever Manfredi or Boston 2024 say, the reason to build temporary isn't cost. The reason is that under current IOC spending regulations, operating funds can only be used to pay for temporary facilities. If you want to keep public money away from this venue, it pretty much has to be temporary. You'd think the Globe would, you know, read the Boston Business Journal article on this same subject and include that nugget of critical information. Or perhaps the Boston.com article that quoted it.