Why would I need to make an account on that instance? I haven't tried yet but it looks like I can respond even with my account from this instance too.
You don't need to. You can view and interact with other instances. The only case where this doesn't happen is if your home instance is defederated from the instance you want to interact with.
Also side note, but unrelated, it does seem harder to find communities, I searched Android on Connect and got relatively little. But I found this Android one by checking specifically on Reddit. Maybe that can improve some way in the future.
If I'm not mistaken, at least on the browser, once someone searches for a new community, it gets federated and then it should show up when you search it. For example: someone in lemmy.world searches for ! android@domain, now it's federated with lemmy.world. Now anyone from lemmy.world that searches for 'android' will find !android@domain, without having to put the whole address in the search field. BUT, this could work differently in connect, so I'm not sure.