The two camps seem to be:
-->Interprets page 1 as she was out hunting for guys, and then sloppily hiding it
-->Interprets page 1 as her teasing her junior with a dirty pun (chinPO (penis) ==> sanPO (walking for leisure))
While neither would really be out of character, I have to lean to the latter.
Teasing him with a pun like this is pretty par for what we've seen of their relationship, and there's no hint of embarrassment, like one would assume if you slipped up like this.
Usually for puns like this, people have to think of different ones with a similar meaning, it's a huge pain, I can sympathize why the TL's went for the more direct approach, though it does paint the MC in a slightly different light (removes the subtle relationship building/ attraction stuff between MC and Kouhai).