OK, here are the details.
The user must have posted the contents into the post from elsewhere. The source had this code on the top.
<div id=":e1z">
<div aria-label="Message Body" aria-multiline="true" contenteditable="true" g_editable="true" id=":e23" itacorner="6,7:1,1,0,0" role="textbox" spellcheck="false" tabindex="1">
I removed this code and the post is now normal and working.
Thank you everyone for the help. Awesome community!