I agree. There are actually 7 varieties for 1982 Lincoln cents plus the single proof (1982 S) is a Large Date Copper Proof only 3.11g. You will notice that its only the 1982-D small date that is only in zinc, and so if found on copper its a rare error with only two examples found. The others all can be found on BOTH zinc and copper planchets normally and only valuable in certain cases like a very high grade such as if you look at PCGS or NGC website price guide or has some other reason like its another variety or error. Copper weight around 3.11g while Zinc weight around 2.5g.
It's theorized that the 1982-D Small Date copper penny was created when a brass planchet, or prepared coin blank, was left in the Mint's coin hopper by accident and was inadvertently fed into the coining presses. At least two (and perhaps many more) were unknown — until the first one was discovered by Paul Malone on November 23, 2016. He found it while sorting his 1982 pennies. It was the first-ever reported discovery of a 1982-D Small Date penny.
What's amazing about this coin is that it took nearly 35 years for it to be found. And what's even more incredible still is that there are likely more out there just like it waiting to be discovered.