Putting aside blow torches and ass doctors...
While I agree with Dave that it's possible you just removed wax, I think it's equally possible that you pulled stain with your magic eraser.
As others have mentioned, a magic eraser is an abrasive and will remove material. I have seen it posited on other forums that magic erasers generally work out to an equivalent of 3600 grit wet sandpaper... but that can vary widely depending on how wet the magic eraser is and how much elbow grease is used. For these reasons I only use magic erasers to remove oxidation from vulcanite stems, and for cleaning up acrylic stems.
I've found that the simplest way to remove smoke and tar build-up from the smooth rim of a pipe bowl is to stand the bowl rim down in distilled water for about two minutes. After standing just the rim in water I use a cotton lint-free cloth (like a kitchen towel or tea towel) to wipe away the tars and oils. Wash rinse and repeat until complete.
If you want to bring the top of the rim back to the same colour as the rest of your pipe you could do the following:
1) Wipe the exterior of the stummel down with 99% isopropyl alcohol to remove oils, stains, and wax
2) Using a VERY LIGHT tint of aniline dye mixed with 99% isopropyl alcohol, tint the pipe such that the rim top blends with the stummel.
3) Buff the pipe with a dunhill pipe wipe, or with a wheel and carnauba wax.
Matching stain colour is a bit tricky at first. I generally use Fiebing's light brown or dark brown starting with two drops of dye to one eye dropper of isopropyl alcohol.
You can, of course, leave the rim lighter colour than the rest of the pipe. This is an aesthetic choice. The rim will darken over time as you smoke the pipe. But it might be off-colour from the rest of the stummel for quite a while... or forever.
-- Pat