Open Source Licenses are granting rights to do things, that --as worded in GPLv3-- "without permission, would make you directly or secondarily liable for infringement under applicable copyright law".
Your question can be broken down into 2 parts:
- Is copyright law relevant for the interaction with Ethereum smart contracts?
- Who is the rights holder that defines the legal terms?
Smart contracts are described here. As you can see, smart contracts are not part of the Ethereum codebase, they are more like a macro within a spreadsheet, and that has its own copyright, independent from the platform that is used to edit/store it (i.e. independent from the copyright of e.g. Microsoft Office, LibreOffice, GoogleDocs, ...).
It is the nature of a public blockchain, that it is replicated many times, one replica for every node. The content of the blockchain is public, any person with an Account can read the entire content. Anyone who puts information on a public blockchain agrees to that (and should own all rights that permit such publication).
As you can see here, smart contracts have a SPDX license identifier tag, which --if present-- may tell you what you can do with it.