Those lines in ox-html.el cause (among others) the hovering "Java" tag:
pre.src:hover:before { display: inline;}
pre.src-sh:before { content: 'sh'; }
pre.src-bash:before { content: 'sh'; }
pre.src-emacs-lisp:before { content: 'Emacs Lisp'; }
pre.src-R:before { content: 'R'; }
pre.src-perl:before { content: 'Perl'; }
pre.src-java:before { content: 'Java'; }
pre.src-sql:before { content: 'SQL'; }
Those are all languages defined, there is no "Lisp" or "Common Lisp".
When you test-add the line
pre.src-lisp:before {content: 'Common Lisp'; }
to the exported CSS file, you'll see a "Common Lisp" hover.
I wouldn't classify this as a bug, though you're right, a language name ought to be displayed for supported babel languages.