Average pace calculation for run workout seems incorrect

I went for a brief run and noticed the average pace per KM seems to be incorrect. First KM 5:29, second 5:11, then for the few metres between finishing the run and stopping the workout 5:16. The average of 5:22 seems to have taken all 3 KM and divided by 3, which I don't consider to be correct. It does not seem to factor in the shorter length of the last KM. If, for example, the last 'KM' (in reality a few metres) was 10:00 the average would be brought up significantly. An average per KM should be exactly that - whole KM or only allowing a relative proportion of a shorter than 1 KM distance to influence the overall average. Am I misunderstanding something here?