Discovered in 1989 by miners quarrying limestone near the city of Mengzi, the fossil remains haven't been studied until 2008. They lived in China at the end of the last great Ice Age from about 15,000 to 11,000 years ago, during a very cold period. They have a curious mixture of modern and archaic human traits but have yet to be classified as a new species. Among those archaic traits are the heavy brow ridges, thick skull bones, lack of a chin, large molar teeth, moderately sized brain and primitive features in the parietal lobes.
Details of the scientists findings can be read in the journal PLoS ONE.
... looks a lot like G or H from the Talk Origins lineup picture:
(G) Homo erectus, Dmanisi cranium D2700, 1.75 My (H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My
The other skull shown is not so easy to compare, however they have a graph showing it with a higher forehead than erectus. They also say:
Vault thickness measurements are presented for LL 1 and MLDG 1704 and compared in Table 5. At bregma, LL 1 has a thick vault (10 mm), being most similar to the H. erectus (ERECT) mean (9±2 mm; z0.49). While its value is within one standard deviation unit of the EUEHS sample mean (7±3 mm; z0.94), it is significantly different to the NEAND mean (7±1 mm; z2.89, p0.006).
Certainly there has been time for some phyletic evolution if there is a continued branch of H.erectus in the neighborhood.
It will be interesting to see how further information adds to the picture.
There are a couple of things I thought about when reading the articles and looking at the morphology:
Are these traits due to hybridization? Or a surviving population of later Homo pushed out of North Africa by Homo sapiens?
If they are due to hybridization, could we expect that certain cultural traits might be carried forward? With a probable low population pressure from surrounding (probably dominant) cultures, could we see artifacts that share traits with earlier Homo erectus populations?
I would expect that these examples more closely resemble cladogenesis and the further branching off of hominin species (consider the diversity within Africa prior to the migration of Homo sapiens), if they are not due to hybridization.
I expect that a lot of questions would be resolved if they are able to extract some DNA from the remains.
As you say, H. erectus has no business being in that area at that time. But, we do know that Pleistocene H. sapiens was quite morphologically diverse prior to their expansion into Eurasia.
It would be exciting to see a surviving population of divergent H. erectus, but I suspect not, considering the lack of H. erectus fossils within the transitional time. Of course, absence of evidence does not necessarily constitute evidence of absence.