In this example code, there are actually numerous declarations that do not have any explicit isolation and are relying on the default. Perhaps especially relevant for the explorations you are doing here, hibernate is picking up the default of nonisolated.
You are, of course, free to not want to rely on any implicit behaviors. That totally up to you. However, I do want to point out that, at least today, an explicit nonisolated is not identical to implicit in all cases. It is not a showstopper, just something to be aware of.