I'm creating a Super Mario level editor, would it be considered as a "remake" of SMM?

[Izerin]

You'll be fine, I guarantee it. There's some phenomenal level editors out there, some of which existed long before SMM. Heck, if you go to the MFGG Hall of fame for the most recent years you'll see a fantastic example, "Yoshi's Fabrication Station". One of my favorites as a young'un was Mario Builder, which is sufficiently aged that the link I provided is an Internet-Archive link.

If the Nintendo Ninjas are willing to let these things fly, I imagine you'll be more than OK. It's actually surprisingly uncommon for Ninty get aggressive with fangames unless they're a production-grade remake (like AM2R was) or Papa Shigeru woke up on the wrong side of the bed.