The — character is the biggest cause of suspicion. It's difficult to type manually so most people - myself included - substitute the easily typed hyphen.
I know real people do sometimes use it, but it's a smell.
I think some software will automatically substitute "smart quotes" for regular quotes and an em-dash for a double hyphen -- I know MS Word used to do this. Curious if any browsers do. This comment was typed in Brave, which doesn't appear to, but I didn't check if Chrome or IE or Opera does.
The comment was not wrong though so I am not sure I understand if flagging it for the sole "it was most likely written by the use of AI" reason is completely valid.
I know real people do sometimes use it, but it's a smell.