For the sake of brevity, you could just have responded with "That is true."
If you mean by wrong that nobody has the entire truth entirely correct (save God if He exists) than sure, everyone is at least somewhat short of the truth in regards to a modeling of the universe (although somebody can be entirely correct in regard to a mathematical statement). However that hardly means that all models are of equal use and equally close to the truth...which would imply that progress in the sciences was not possible.
Again, for the sake of brevity, you could just have said, "I know what you mean."
An aside: (save God if He exists)
I absolutely believe, and know, that God exists (IS).
To save materialism from the devastating blow to its core principals dealt it by the big bang, one is forced to expand the very definition of nature to extend beyond the universe itself...
Is the Universe finite or infinite ?
...and one must by blind faith cling dogmatically to the presumption that nothing beyond the universe resembles a super-nature.
Using religious terms to describe how an 'atheist' thinks seems odd.
In regard to "if He exists", I am speaking from a perspective of argument which does not assume He exists or that Christianity or the Bible are necessarily correct. Although I am convinced He does, and that Christianity is correct (by which I mean Christ's version of Christianity, as all us mortals have a less than perfect understanding of it), many Freepers may not share this belief and some of those may be reading what we write. Assuming the Bible is correct was never very convincing to me as a reason to believe the Bible when I was an agnostic. I like to mention some of the things that convinced me along my journey in the hopes that it will help someone else discover the truth.
I like to use the same terms in describing the doctrines or theories of any philosophy...to put them on an equal footing in regard to irrational prejudices built into language and habit. Particularly since so many modern materialists seem not to rationally consider whether a philosophy is correct or not but whether it fits in the "religious" bucket (which they meet with irrational skepticism) or the "modern" bucket (which they meet with irrational gullibility).