how is it determined if there's an uptick or downtick?

Has it been coded such that if there's a new higher bid price, it's counted as an uptick? But if there's a new higher ask price, it's not counted as an uptick?

If it's not coded this way, don't you think that would be erroneous since new bid prices are provided by liquidity providers only when there's a buy order? So when the ask price goes up without the bid price also going up, it's wrong to assume a buy order has occurred, no?

actually, i was able to confirm it does behave the way i had hoped by seeing that volume indicator shows values that equal volumeUp+VolumeDN