Trunks doesn't recognize 19 and 20 mentioned the lab earlier, that's all pointing to one thing. But this chapter was pretty good, I will admit the constant use of the senzu beans already does feel a little cheap, and robs a lot of dramatic tension. Still, I like Gohan saving Piccolo, and it's nice to have Piccolo get his time to shine too, making easy work out of 20 here.