They can open source it and still keep the copyright. I mean it is not automatically GPL just becouse they put it on a public git server.
Which it probably does.
"...Versions of Internet Explorer before version 7 stated "Based on NCSA Mosaic" in the About box. Internet Explorer 7 was audited by Microsoft to ensure that it contained no Mosaic code,[39] and thus no longer credits Spyglass or Mosaic."
oh wow, thanks for the correction, cant beleive i missed that