User blog comment:DaNASCAT/Technical Update:July 15, 2015/@comment-11733175-20150716160156/@comment-24473195-20150716161442

It is probably part of the portable infoboxes' code. I'm guessing that they only enabled it for specific wikis for bug testing. Can't you simply ignore it or mark it as "not an infobox" or  disable it on your personal js?

It is not even available at Community central. So it is a limited beta testing.

Edit: I just looked at a couple of Top wikis' Template:infobox. It only seems to be enabled in really popular wikias, top 10/20 of the WAM list.