What? Who is asking for him to make a definitive statement?
The point being that Smith is likely still using a brace in some capacity and when Jones made the comment he said, he truly didn't know if in the future (meaning August, the season, etc.) Smith would have to wear one. But at this point in time, they were comfortable with the idea that he could play with one if needed.
Secondhand or not, I suspect the Cowboys have a very good idea if Smith is still utilizing a brace, if that brace is only needed for certain workouts, etc. He's also monitored by doctors and they would also provide information to the Cowboys. So no, while Jones hasn't stood next to Smith and watched him workout, I suspect the front office has a very good idea of what, if any, limitations Smith still has, brace usage, etc.
Has he made progress? Absolutely. Can he line up in August for full contact practices without a brace? That's clearly unknown. And the fact Jones even mentioned that possibility in late March seems to indicate that at that time, Smith was still utilizing a brace in some capacity. The Cowboys would absolutely know in March if Smith was still using a brace full time, part time, etc.