Is that how it works? In that case I have some business ideas ...

Some do consider it vegan, same as the "freegan" subset. There's even at least one influencer who is a bit infamous for it But there's also a few problems with this line of reasoning. It still normalizes the idea of the consumption of animal products, so it's a slippery slope at best. It's also not scalable, as soon as probably even a modest proportion of people would adopt such a diet, demand would quickly start to surpass supply which would incentivise the artificial production of more road kill.

And then there's just the why? of it. Like if we're talking about extreme situations like starvation and poverty where there is literally no other choice, okay that would make sense. But otherwise, what is so wrong with eating plants that someone would go out of their way to eat carrion instead? With the likely putrefaction involved we are talking about literal self harm to avoid eating some good ol grains and beans.