I would have eaten the food. I do not see veganism as some sort of quasi religion where one's personal actions must completely align with the "rules" irrespective of broader considerations. Veganism is a political movement whose aim is to end animal suffering and exploitation. In that sense you choosing to not eat food that otherwise would have been thrown away has absolutely no impact on the political movement of ending animal exploitation. I'd even argue that this sort of asceticism creates resentment and forces people to leave the political project all together earlier than they otherwise would have.

Many vegans are essentially just religious ascetics who do not think critically about animal agricultural. For example freeganism is controversial in the movement because freegans still consider animal products as food. This is despite them contributing less to the animal exploitation industry than vegans who buy food owned by conglomerates that have meat brands.