A CPU is effectively an interpreter itself, albeit one for machine code; seen this way, Sparkplug is a "transpiler" from Ignition bytecode to CPU bytecode, moving your functions from running in an "emulator" to running "native".
I like the reasoning in the sibling comment:
> So if you want to understand what other people are saying about "compilers" you should keep in mind that the standard definition includes what you are calling "transpilers".
Really, the main disadvantage of saying "transpile" is that it implies you don't know what "compile" means. In a context where that wasn't an issue -- e.g., if I heard it from one of my coworkers, who certainly know what a compiler is -- I would just think they liked the neologism.