Secular people don’t use this kind of language:
This speech was after the one you mentioned, and had no allusions to the kind of secular outlook you proclaim.
As gov. general, he had to convince the crown that pakistan was to care for minorities; this in no way negates the fact that a) aspects of Sharia law were already woven into the state apparatus and b) he advocated some form of Islamic statehood, even if it was ill defined.
Personally, I doubt Jinnah knew what Shariah was, and personally kept away from the subject as it was no doubt a can of worms.
A single phrase from a single speech is simply far outweighed by laws on books, and multiple pronouncements of his notion of “Islamic state”.