I started a restaurant, but never considered it a “startup”. It was new to the world, not a chain, and though successful still a small business. It was complicated to figure out but there were a million examples to work from and you start cash flowing rather quickly.
I also have a startup - because they are new products that have not been done before. There are many complicated things to figure out - even with simple products! I agree with Paul O’Brien’s answer although the fail rate for restaurants and startups seem to be nearly the same. Startups often require more money though.
In a startup you work for a long time without making money as you need to prove the product or the concept. If managed correctly, once it takes off you can scale up quickly. With a small business (like a single location restaurant) there is only so much money that can be made. If a small business is unique enough and loved enough, you can franchise it to become larger but it is a different kind of risk/reward.