Say What?

As I was walking the 4 blocks from my work to my car downtown this evening, a scruffy-looking man fell into step beside me. He turned to me and eyed me from head to toe and back up again, and then remarked "I bet when you was in high school your nickname was Shorty!" This sort of remark falls into the category of the "less-annoying" things that people usually say to me, so I laughed cheerfully and kept walking. Then he eyed me again and said "But I bet you changed all that though" before he walked on.

I generally brush off these sorts of encounters as they are very brief, but I couldn't help wondering as I walked the rest of the way to my car: what the heck did he mean?