That looks like someone used a LI and Ordered List, in the original instead of UNORDERED (and no mark).
Calibre conversions can look for strings to Create Chapter Headings.
Found in Conversion: Structure detection
Code:
//*[((name()='h1' or name()='h2') and re:test(., '\s*((chapter|book|section|part)\s+)|((prolog|prologue|epilogue)(\s+|$))', 'i')) or @class = 'chapter']