Is there such a thing as an "ERC20 compatible Ethereum address"? I believe the answer to be no, but just asking here to confirm.

I think the answer is that it is just the software interacting with the address that is ERC20 compatible or not, not the actual address. It doesn't matter what software generated the address, and it is fine to generate the address using any software for doing so. As long as I have the private key for the address, I can import that address into an ERC20 compatible wallet software, such as myetherwallet.com, and interact with the address in an ERC20 compatible way.

It means that the title for the e.g. the article How to generate your Ethereum ERC-20 compatible wallet address is slightly misleading, because it sounds like there is something special with the actual address generated. But how could there be, since an address is just a key pair?

Have I understood or not?
This is correct.

Any Ethereum address is compatible with ERC20 tokens (even a contract address).

There is also the ERC223 standard, which isn't finalized, and if approved would allow contracts to accept or reject specific tokens. In such a case, contract address validity would be a valid concern.

However, for ERC20 tokens, there is no such issue, and every address works (although some tokens include safeguards against sending to 0x0000000000000000000000000000000000000000)