Was there an actual person Rabi Tanchuma attributed to writing the medrash that goes by this name? Do know anything about him?
See this other Wikipedia entry that states:
Tanhuma bar Abba (Hebrew: תנחומא בר אבא) was a Jewish amora of the 5th generation, one of the foremost haggadists of his time. He was a pupil of Ḥuna bar Abin (Num. R. iii.; Gen. R. xli.), from whom he transmits halakic (Yer. Ḥal. 57d; Shab. 10c) as well as haggadic sayings (Yer. Pe'ah 15b; Shab. 11d; Ab. Zarah 43a). He received instruction also from Judah ben Shalom (Midr. Teh. to Ps. cxix. 2) and R. Phinehas (Yer. Sheḳ. 49d). According to W. Bacher, he resided in Nave, a town in Peræa (comp. A. Neubauer, G. T. p. 23).
Midrash Tanhuma was named after him because he was the first person named in that Midrash, but, the Midrash itself was written during the course of many years. This is common, like Avot D'Rav Nattan which was named after him for a similar reason.