Of course the second one is more likely to be right, but how would a computer generally know that?

By both people having gone in that room and seen it was white for the past 300 days in a row, then one day one person says it's bright pink.

That one day of pink is a statistical outlier, and it disagrees with the other computer which is statistically more likely, so we choose the computer that said the room was white and we make a note about how the other computer was wrong.

there is no algorithm to detect which of two outputs seems more likely.

Yes there is, it's broadly called Regression analysis.