I noticed that too! Only recently in two otherwise perfectly fine stories. That kind of punctuation mistake drives me crazy because it tears me out of the narrative every single time someone opens their mouth.

I've actually started to wonder if that is how they do punctuation in some country. I know that we do it differently in Germany. Here it would be:
"Hi, guys", John said. (I *think*. I actually know English punctuation better than German.)

I learned that rather significant little difference in fandom, not in high school as one would expect.