No, I replied from feddit.org.

On lemmy you can see where the account is from

and you should be able to see Kissaki@feddit.org.

I tried to reply to my long comment from mastodon.social, but it didn’t show up. I assume lemmy.world blocks replies from mastodon.social.

Given the diverse nature, instances can control to what degree they connect to other instances within the Fediverse.

One instance may block another because of spam or extremist or illegal accounts or content. Or they may allow interaction but only for those explicitly seeking it out instead of showing it within their own interface. etc

On Mastodon it looks like this:

My reply (second screenshot) did not show up here on Lemmy. I assume because lemmy.world blocks replies from mastodon.social.