I don’t know how things are in the US, but in the UK the majority of labs also measure haemolysis and suppress potassium (and other results) if it is above a certain threshold for haemolysis.
There are other potential causes of factitious high potassium results. If the sample is kept at a cold temperature (refrigerated or transported a long way in an unheated container in cold weather) the active transfer of potassium into cells is slowed and causes a rise in serum potassium. Likewise, leaving a sample uncentrifuged for too long (24 hours or more) will cause high serum potassium. Full blood counts are usually taken into tubes containing potassium EDTA, so if the FBC sample is taken first, the biochemistry sample can be contaminated.