He has taken upon himself something that is not his.
To interfere in a matter that does not concern him. To deal with a matter that is not related to him. To 'involve his father' in matters that have no connection to him.
("A sick man struck them, and he said to them, "Tell me, my rabbis, how shall I be healed?" They said to him, "Take such and such until you are healed." The man who was with them said to him, "Who struck him while he was sick?" They said to him, "The Holy One, blessed be He." He said to them, "And you have gathered yourselves together in a matter that is not yours. He struck, and you are the healer." - Midrash Samuel (Buber) Section D)
Translation
Expression (Hebrew)
הִכְנִיס עַצְמוֹ בְּדָבָר שֶׁאֵינוֹ שֶׁלּוֹ
Definition (Hebrew)
הִתְעָרֵב בְּעִנְיָן שֶׁאֵינוֹ שַׁיָּךְ לוֹ. טִפֵּל בְּדָבָר שֶׁאֵינוֹ קָשׁוּר אֵלָיו. 'תָּחַב אֶת אַפּוֹ' לִדְבָרִים שֶׁאֵין לוֹ קֶשֶׁר אֲלֵיהֶם.
("פָּגַע בָּהֶם אָדָם חוֹלֶה, אָמַר לָהֶן רַבּוֹתַי אָמְרוּ לִי בְּמָה אֶתְרַפֵּא, אָמְרוּ לוֹ קַח לְךָ כָּךְ וְכָךְ עַד שֶׁתִּתְרַפֵּא, אָמַר לָהֶן אוֹתוֹ הָאִישׁ שֶׁהָיָה עִמָּהֶן: מִי הִכָּה אוֹתוֹ בְּחוֹלֵי?- אָמְרוּ לוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא, אָמַר לָהֶן וְאַתֶּם הִכְנַסְתֶּם עַצְמְכֶם בְּדָבָר שֶׁאֵינוֹ שֶׁלָּכֶם, הוּא הִכָּה וְאַתֶּם מְרַפְּאִין"- מִדְרַשׁ שְׁמוּאֵל (בּוּבֶּר) פָּרָשָׁה ד)