Congresscritters, and their staffers, are notorious for slip of the lip.
Sometimes it's calculated to show our hand, and let the other party know we're dead serious.
I watched in horror as Colin Powell did the same thing at the U.N. one afternoon.
I could almost hear the DCI thunking his head against his desk in Langley.
Intel is sometimes allowed to be promulgated to the other side when the value of doing so outweighs the loss of that source or means of collection later on.
F-101 Voodoo and U-2 photo recon images from Cuba are but one example.
That's not saying Feinstein was correct in what she did, but there is indeed more to a given story.