Allow me to explain why the idea of European contamination is ludicrous. This particular mtDNA haplogroup is thought to have split off from our ancestral lineage at least 150 thousand years before the birth of mitochondrial eve. It would be easy enough to pass it off as a false result if we didn't have evidence of another member of the same Haplogroup that LM3's DNA belongs to. An mtDNA haplogroup that is ancestral to Mungo Man's iserted itself into Chromosome 11 of one of our own universal ancestors, and it is present in all populations and ethnic groups worldwide at a global percentage of 39%. This ancestral mtDNA haplogroup is frozen in time, no longer diverging as a normal mtDNA haplogroup would, so all 39% of modern humans have the same exact version. That version is from several versions BEFORE the divergence of it's descendant haplogroup, which was found in Mungo Man.
If it were European Heidelberg, how did an Asian Heidelberg's DNA get into a European?
What's more, the highest rates of the LM3 insertion on Earth are found in indigenous people of Japan, Papua new Guinea, and Columbia South America. These three people have been proven to share nuclear DNA that they do not share with any other people on earth, save a few other Austronesian populations in the Pacific. This common ancestor is not reflected in their mtDNA or Y DNA, but is only reflected in their nuclear DNA. The common ancestors of these three people assimilated a population that possessed the LM3 insert or mtDNA haplogroup LM3 itself. That population almost certainly lived somewhere in the Pacific, which is the common ground between these three populations. Sundaland and several other massive expanses of land existed in the Pacific before the end of the last Ice Age. And where is Mungo Man's ancestor from? That's right, got to be the Pacific. There's just no other way for him to get to Australia.
If a blurred or contaminated mistake from an extinct archaic from the Pacific looks not just like the mtDNA of extinct archaics from the Pacific, but like the extinct great-great-great-grandson of those extinct archaics from the Pacific... well that would be the craziest coincidence that world has likely ever seen.
So what's the better answer?
As John Hawks showed in the First Peoples documentary on BBC, Homo Sapien Sapiens was born not from one group of Heidelbergensis, but several subgroups of Heidelbergensis. The LM3 genome lived with us in or near Africa at one time, most likely around 150 thousand years ago. Without borrowing genes from Mungo Man here and there, we would not be anatomically modern. Without borrowing genes from us, neither would have been Mungo Man.
There were at least two genomes of Anatomically Modern Human living in the Upper Pleistocene, and none of them could have been Anatomically Modern without the others. What's more, none of them began as Anatomically Modern. They were borrowing and trading genes, and what we wound up with as modern traits is what these two or three groups preferred collectively in sexual partners.
After we obtained a bit more Neanderthal introgression than the LM3 genome had aquired, and after the explosion of Toba had severely diminished and scattered its population, we drove what remained into the Pacific and then to extinction, but not before taking everything we wanted from it.