[GuidoK]

hmm yeah looks like thats potassium free (at least in high quantities). So trace elements of potassium might not be the best marker.
I looked up some more and they mainly contain sodium based salts, although it seems that each manufacturer uses different ingredients, sometimes displayed with "Aqueous solution of inhibiting salts" rated "not classified, so that could be anything really as long as its not harmful. Some do seem to contain potassium (like potassium ethylhexanoate and such) but certainly not all coolants indeed. Its a very mixed bag.

But it would still be bad if hot air from the fan and engine would reach the intake.
Usually everything is done to prevent that, so I still think that there are numerous other ways sodium can get in an oil analysisreport.