Steaming aircraft.....
Part of the De-Iceing process (as distinct from the Anti-Iceing process) is the application of very hot fluid to the airframe. This will probably account for the observed 'steaming'.
Only a few days ago in Seoul, whilst awaiting our own de-iceing, observed many aircraft leaving the de-iceing pads with steaming fuselages, and fuselages definately don't have aircraft Anti-Ice.
Regards,
Old Smokey