My reply is below. I didn't try to be funny when I wrote him back, I just kept it simple and sincere. I've never been accused of plagiarizing Bob the Angry Flower before, so this was a refreshing change from some of the other fine folks who have contacted me in the past.
*note:* It's a pain to embed clickable links in that email screenshot, so here they are instead:
When I first launched my website, most of them followed that format, e.g. Things Bears Love and How to Ride a Pony. I did that primarily because I wanted them to all go into a book with a theme built around numerical lists full of nonsensical, silly things. I still make comics like that occasionally, but now I tend to write about more topical stuff like nature, food, technology, illustrated stories, and subversive humor.