The Maharshal’s “Rishonim” is different from ours. Let’s not forget that there was never a meeting when the names were doled out. Anyone familiar with the Sefarim from the Maharshal’s time can see that they use “Rishonim” sometimes for Amoraim and sometimes for the early Rishonim. The Maharshal or Beis Yosef think of the generation of the Rashba, Ritva and Rosh as Achronim. And yes, this Tosafos does seem to be compiled in those later generations.
In truth, Tosafos’ mention of the Tur is in brackets, so perhaps it is not actually from the author. Usually though, brackets in Gemara and Tosafos mean that it should be read as part of the main text, according to someone. The Tosafos I’m referring to is the end of the Dibur, Lan Bitaaniso on 11b.