MartinJD that's correct. Composer warnings are usually based on everything you have currently installed, not only the extension you are currently adding or updating.
In this case the zendframeworks warnings come from Flarum core itself. We will update them in the next version.
If you see an extension name being reported as abandoned however, you might want to take action as this one was probably manually installed by yourself 😉 There's rarely a security risk, but if it's abandoned it usually means it no longer works with the latest Flarum version and could break things if enabled.