Well, for starters, I'm actually a girl, but more importantly, this wouldn't make sense as the "end" of this series, because Astolfo's reaction makes it pretty clear that A) He's never seen Gudao's dick before, and B) Gudao hasn't nailed him with it yet. He wouldn't be surprised if he'd seen it before, and he wouldn't be so much of a tease about it if he'd already had sex with Gudao. Also, I'm pretty sure that this scene is set in a bathroom (like, they're at side-by-side urinals), so even if it was the end my prediction would still have been false because it's not exactly "walking in on" Gudao.