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We study the crystal structure-mismatched, quantum dot-like (QD) composite metamaterial based on rock-salt narrow gap PbTe and zinc-blende wide gap CdTe. In the case of PbTe/CdTe QDs the quantum effects are observed for dots with dimensions of the order of 100 nm even at room temperature making this material system a promising candidate for mid-infrared applications. Using molecular beam epitaxy technique and utilizing difference in crystal structure of both semiconductors a variety of samples containing PbTe nanostructures with complicated morphology embedded in CdTe were obtained. Investigated nanocomposite PbTe/CdTe samples exhibit unusually strong and surprisingly narrow (about 5 meV) mid-infrared photoluminescence emission (250 meV) in contrast to the spectrally wide luminescence of a typical ensemble of PbTe/CdTe quantum dots measured in similar temperature (about 100 K) and excitation power conditions (400 microW). For excitation power exceeding 500 microW additional emission in energy about 15 meV lower than previous one appears, which dominates PL spectrum for excitation higher than 800 microW. This line, not reported for such kind of QDs yet, exhibit non-linear dependence of amplitude on excitation power. We discuss the observed behavior of photoluminescence considering presence of two-dimensional electron gas with high electron mobility and carrier density up to 10^19 cm-3 spontaneously formed close to the polar CdTe/PbTe interfaces. As estimated plasmon energy in our samples (240 meV) matches well the energy of observed emission, non-resonant coupling of photons with interface plasmons mediated by LO phonon is most possible explanation of unusual enhancement of PL from studied PbTe/CdTe metamaterial.