I’m guessing he had either an XR250r and didn’t know the difference or he had a Cr with an Xr engine.....What is the actual issue you're experiencing? You bought a bike, but it has never ran in your possession? It quit when riding it? Previous owner said the CDI is bad?
I cannot imagine the timing between a 4T engine and a 2T would be similar.
Can you take a picture of this bike? Can you take a picture of the connectors that went to the CDI?
And now I’m doubting myself ffs, after looking at xr250 cdis on eBay the one I have looks about 10 years earlier from an 84-86ish