Halachic discussions in the Gemoro can end with the word תיקו. According to one view in Hebrew Wikpedia it stands for
תשבי יתרץ קושיות ובעיות. שמשמעותן: השאלה תעמוד ותוכרע רק כאשר יבוא התשבי -אליהו הנביא
The question will be answered when Eliyohu comes.
The Gemoro in Shabbos 108a records a question asked of Rav Nachman bar Yitzchok whether tefillin cane be written on the skin of a fish. Rav Nachman answers
אם יבא אליהו ויאמר When Eliyohu comes, he will tell us.
The Gemoro asks what this last statement means and Rashi comments
היתר ואיסור אין תלוי בו דלא בשמים היא
(We do not rely on Eliyohu to teach us whether something is) permitted or forbidden. It does not depend on him because the Torah is not in heaven.
How does Rashi's comment fit with the understanding of תיקו referred to above?