1947 "Un Balboa" From Panama - Fake

Yes if the coin is magnetic it is not a copper silver alloy.

Regarding the existence of numismatic forgeries of the 1947 Balboa - they have been around for a while at least 25-30 years.

Most recent fakes including the kind typically seen on ebay come from China. They are injection molded and are edge AFTER they are cast (in part to cover the seam). The Chinese edge these coins using two different (incorrect) methods that leave clues. Often they are edged with a ring die. A stack of fakes is pressed through a tapered ring with the reeds cut on the inside circumference. These have split tops and the corners are often ground down to eliminate clues. The other way to apply the reeded edge incorrectly is to roll the coin against a die which creates an overlap in the reeds - both are adequate to identify a fake even without a magnet.