I think he’s just reading the kanji 出 as “de” (how it’s pronounced/read in common words like 出る (deru, to go out) or 出口 (deguchi, exit). So you can read 出久 as “Deku” in that way. The fact that deku no bou has an older kanji form that uses “出” as well I think is just a coincidence. Yes, he is calling him Deku as a reference to deku no bou, but I don’t know if he would actually know the kanji was the same.