This observation is probably correct.

A “subnet” is simply a predefined and dedicated space of IP addresses given on any type of network (most likely public or at least not-private).

What you probably want is a Private Network (or Private Cloud).

The “cloud” industry has really run rampant with standard networking terminology being used in Marketing and UI labels in ways unaligned to standard definitions, so double check.

But if they have a separate product for VPC/VPN, then the above is most likely true for them.