Hi,
I believe you looked at the leaf certificate and have seen the basic constraints extension there, right?
To answer this question, you have to take a look at the root CA's certificate. In the root certificate, you will be able to see: "CA:TRUE" without a pathlen constraint given. This means that the root CA is allowed to issue intermediary certificates.
Additionally, if you take a look at the intermediate CA certificate, you can see CA:TRUE with pathlen set to 0. This means that this is a CA but it is not allowed to issue any further CA certificates.
I hope this makes sense and clarifies the answer. Let me know if you have any additional questions :)