"The secret weapon" I think makes reference to Paul Graham's essay Beating the average: http://www.paulgraham.com/avg.html and he probably thinks that Smalltalk gives the same kind of "unfair advantage" as Lisp did in Paul Graham's article.
According to some studies, Smalltalk seems to be very productive: https://www.cincomsmalltalk.com/main/2022/07/need-productivi...
http://www.ifpug.org/wp-content/uploads/2017/04/IYSM.-Thirty...