It's possible that he didn't actually do that, and was only blogging the fantasy ("Man, I'd love to troll her with increasingly stupid cat posters until she lea

It's possible that he didn't actually do that, and was only blogging the fantasy ("Man, I'd love to troll her with increasingly stupid cat posters until she leaves me alone ..."), but it's also possible that we see the response after being frequently asked to do Free Work as a "favor" for coworkers who either won't accept "No" or don't understand that it's inappropriate to depand such work. If we take this at face value, she could have asked more nicely, and he could also have followed the "F you, pay me" principle, and just quoted her a figure. Had he said, "I'd be happy to make you a poster for your cat. I will be able to do it with an hour's work, for which I will bill you $80", he would not have wasted her time, and she could have made something herself in her word processor. (Or, she'd have said, "Awesome, here's eighty bucks".)