I think there's a setting in your controls that makes these record. I've edited my spelling/punctuation on several posts throughout the years with no record.
Overall I'd rather see everyone's edits time-stamped. I hate seeing that edit on my posts, but I hate typos more.
It's a user-defined control. We have the Board set to allow users to determine whether the "Edited" line is displayed. When you edit a post, look below the window with the text in it for the line:
"Edit Options Add the 'Edit by' line in this post?"
There is a check-box before "Add the 'Edit by' line in this post?" Uncheck it.