I've made general statements in the comments, not really directed at anyone in particular. I've made replies to what others have said as well, so it could be more than just a note/message to/for the author. A lot of it depends on your purpose in commenting really.
I tend to see the comments section as a way for everyone to interact with each other. Readers are able to share their ideas on where the plot is going next or remind each other of things that have happened to whoever in a previous chapter or to help speculate the answer to certain dilemas found in the chapter/novel. The author(s), or the ones I read at least, enjoy the commentary provided and have occasionally taken those comments between readers and added them into the novel itself (for example, one novel had a character that had gotten a ridiculous nickname from another character and the comments section just blew up with a ton of other cringey/silly nicknames of which some were added in the very next chapter. It was just readers messing around, but the author enjoyed it as well).