Mark 4:31 - It is like a grain of mustard seed, which, when sown on the ground, is the smallest of all the seeds on earth,
I'm just saying here that your peanut butter analogy doesn't quite "stick its landing" as I see it, although I do agree with your overall point about the mustard seed being the smallest in Israel and the fact Jesus was definitely not wrong.
Not only was it the smallest known in Israel at that time, the smallest seed is actually an orchid and would not be considered a grain.
There are smaller grains than the mustard but that would be akin to us demanding Jesus stop teaching His theology and start teaching about teff seeds in Africa (or whatever is discovered to be smaller grains now).
I believe God uses these verses to illuminate a light on our hearts and will our hearts harden over such a minute factoid? Or will we put our hands to the plow and remain faithful in His ministry through us?