Well, they weren't just making things up; there clearly was information that they had, that I wanted, but that they were initially reluctant to give me. At that point ultimate survival did not seem to be the issue, but I had no idea whether the answer to "how long" was going to be hours or months! Even if the statistics they had was something like N=5, that was still (mathematically) infinitely more than the N=0 that I had.
You might have felt that but my impression is that the doctor in question was mostly making up something on the spot. I would guess that the doctor is simply saying that they have never encountered anyone in this situation leaving intensive care within four days and similarly no one who survived needed longer than three weeks. The last answer suggests that they have no actual statistics at all.