That is not true about a prophet under the new covenant. We have a very different relationship with the Holy Spirit than in those days. The Spirit could not dwell in the heart as He does now. Then, if a prophet spoke from his heart, he was false, period. Now, because we have the Spirit in our heart, we can speak from the heart and be true. Bit we can misunderstand also, what the Spirit is saying.
This is why we are not called to judge the prophet, only the word given. I did not say that Jonathan is false, just that some of the word is wrong, or false. In that I hold no judgment on him whatsoever, and truly hope that he grows in this very difficult gift.