Ok, go stand in front of a bus.
2. The comment you replied to did not state that the commentator holds that view, it was merely an observation that they didn't expect certain content in the article.
For example, I might assert that "Tomorrow, the gravitational constant be the same as it is today." This seems like a fact: we have pretty strong theoretical justification for it, given certain empirical evidence, an assumption of regularity in nature, and the continued predictive success of the general theory of relativity. However, if tomorrow the gravitational constant is slightly different to what it is today, then although no (deductive [1]) logical law has been contravened (as would have to be the case if a provable statement turned out to be untrue), my assertion was clearly not a fact.
However, proofs (as in mathematical or logical proofs) are obtained through deductive reasoning, not inductive reasoning, as my statement was. Thus, I would argue, there is nothing wrong with presenting something as a fact which is not provable. Otherwise, we wouldn't be able to assert very much at all: the restricted epistemology obtained would rule out all of science, for starters, and might even cast doubt on certain classes of observation statements.
Of course, you may have meant something other by 'provable' than I do, in which case clarification would be appreciated, since you presumably meant something by your assertion that facts must be provable, and it would be nice to know what it was!
[1] It is controversial as to whether a general inductive logic can be formulated.
I'm sure there's better formal language for this, but we could benefit by making a distinction between "facts in principle" and "facts in practice". Let's say a fact in principle is derived from a priori knowledge, whereas a fact in practice is one that we have accepted and depend on in order to make pragmatic decisions and survive. In principle, I believe that I exist but that I cannot prove objective reality exists. In practice, I accept that objective reality exists and that if I stand in front of a bus I will be hit.