In the turbine world it's extremely common to use segments of engines across various engine lines. Really it's common in the piston world, too (think about the 360 vs. the 540). The most common way of doing it is exactly how GE did this one - take an existing core and then bolt a low pressure section around it. For example, the cores (high pressure compressor/turbine) sections of many civilian engines have been derived from military engines (such as fighter jet engines) and then have a low pressure turbine and fan bolted to it. This reduces development cost.
For this engine, they took the core of the HondaJet engine, and then bolted a low pressure turbine and gearbox to it. The reverse flow works great on a turboprop, since it allows the low pressure turbine and gearbox to all be easily together without a shaft connecting them, which improves simplicity.