My definition of bootstrapping has more to do with the mindset you have while running the company, rather than whether the company actually has investors.
There’s always someone putting money into getting a new business up and running (bootstrapping is not free). Whether that small amount of money comes from the founder’s pocket, family/friends, or an angel investor - the money to pay your AWS bill and other basic services has to come from somewhere.
Bootstrapping is an operational mentality IMO.