Why is it so important to know that Avraham was baking matza when Og came? And even if we need to know that, perhaps so we should know that Avraham Avinu kept a form of Pesach, why did this pertain to Og to the extent that the Torah refers to him forever after as Og, in commemoration of the matzos/ugos?
Antibody or DNA testing can determine the presence or absence of yeast in baked products. A laboratory can determine with absolute certainty that a given baked item was totally unleavened. A perfect, beautiful Matza that was baked for general use and was later determined to be totally unleavened can not be used for the Mitzva of Matza. The halacha of Shimur is that the harvest and the milling and the kneading and the baking must be supervised with the intention of avoiding leavening so it can be used for the Mitzva of Matza. Without this specific intent, you certainly could use it on Pesach, but you would not be yotzei the mitzva.
When Og came to Avraham with his evil plan,he found Avraham baking Matza. Matza is the archetype of proper intent; without the proper intent, matza is just a flat piece of bread. If intent matters in a simple thing like a matza, how much more so in something so deeply powerful and beautiful, in a matter of life and death, good intent can make it even more meaningful, and bad intent can pervert and degrade the entire effect. Og could have learned the lesson of the Ugos. Unfortunately for him, he did not. He is like B'tzeikos shel Nachrim (Pesachim 40a), an example of lost potential for greatness. He was not a Matza, he was a Bulkeh. Bulkeh, the King of the Bashan.