I'm not sure what he had in mind at that time, but Dijkstra was never all that enthusiastic about type theory. He thought it was a promising and worthwhile avenue, but was suspicious of it being treated as a panacea.
"Another thing we can learn from the past is the failure of characterizations like "Computing Science is really nothing but X", where for X you may substitute your favourite discipline, such as numerical analysis, electrical engineering, automata theory, queuing theory, lambda calculus, discrete mathematics or proof theory. I mention this because of the current trend to equate computing science with constructive type theory or with category theory."
=) Sorry, I was being sloppy there - couldn't come up with an accurate and un-platitudinous way to characterize Dijkstra's attitude. There are other places in his writings where he's suspicious of an overemphasis on types, I think his criticisms of Ada mention it for example.
Dijkstra was a big proponent of rigorous mathematical means of establishing program correctness in general, of course, but he didn't necessary equate that with types.
http://www.cs.utexas.edu/users/EWD/transcriptions/EWD12xx/EW...
"Another thing we can learn from the past is the failure of characterizations like "Computing Science is really nothing but X", where for X you may substitute your favourite discipline, such as numerical analysis, electrical engineering, automata theory, queuing theory, lambda calculus, discrete mathematics or proof theory. I mention this because of the current trend to equate computing science with constructive type theory or with category theory."