Currently, the displaytitle field returns by ApiMobileView may contain HTML or plain text, depending on whether {{DISPLAYTITLE}} was used on the page to override the title. In I043b26b82f I clarified that core *always* stores and returns the display title as HTML. Code that uses displaytitle needs to be aware of this. When falling back from displaytitle to the actual page title, escaping needs to be applied to ensure consistency.
Once ApiMobileView consistently returns HTML for displaytitle (technically a breaking change, though it really just fixes an inconsistency), clients that use this property need to be made aware that this is HTML, to avoid double-escaping.