What they meant when they said "planets" was the 8 (previously 9, previously to that 8, previously 7...) known and named planets in our own solar system. A hypothetical "Journal of Planets" that was actually about solar system astronomy wouldn't necessarily have known what to do with a new paper about 51 Pegasi b published 30 years ago. They're thinking "when we said planets, we actually always meant solar system planets, it just never came up until now".

The reviewer of this paper is saying that by biology they always meant naturally evolved cellular biology, not synthetic biology - there's just never been an example of the latter before.

I think the take is wrong, the receiving journals should be excited to expand their scope rather than frustratedly redefine their scope more narrowly, but definitions and categorization are hard.