That's my understanding as well. Someone could try to make your email client img-src-get the plaintext of previously intercepted mails to a remote server, but i

That's my understanding as well. Someone could try to make your email client img-src-get the plaintext of previously intercepted mails to a remote server, but it would be a very "noisy" attack: your typical PGP user would very quickly fall into a panic if they received all their old encrypted mail again, and for some reason the client would constantly beg for external image downloads in apparently plain text mails.