RSRH: So what he means is that there are true things which are not contained in the torah?
You mean like the fact that I am typing on my computer now is not in the torah, but is true?
I think we can all agree to that.
Now, I’m not sure we should equate true with valuable, since the knowledge that I am currently typing on a computer is not very valuable (except to Joseph).
So if he argues secular knowledge is valuable (or as I suspect, he argues it is necessary), then the value must come from something besides its being “true.”