Not defending 'kph' exactly, but I can see how some native metric speakers (in Australia at least) might arrive at that solution on their own. You're right about 'kilos per hour': 'kilos' will always be taken to mean kg. But in speech, 'kays' is a common abbreviation for both km and km/h (confusingly). So 'kph' would be an ambiguous way of writing 'kays per hour'. I have heard a small number of people say K.P.H. as an initialism.

kays (distance) e.g. "Thongs'll do, we're only walking a few kays down the road."

kays (speed) e.g. "Apparently he was doing 120 kays in the Barina. I'll miss him."