Subaru forester xc boxer diesel dpf burnt injectors coding

Wondering if anybody could help. I bought a forester xc 2.0 diesel 2009 model required new engine as crank was broken. A complete engine was sourced (with injectors dpf etc) and fitted to the car. After four week of having the car and doing around 1500 miles I came off the motorway (after driving 5 miles only driving at 60-70 mph) noticed car was blowing out smoke from exhaust, when I drove around the bend to park up noticed burnt glowing bits coming out. Parked up  stopped engine smoking stopped but exhaust tips were covered in white residue, open bonnet and dpf was glowing orange from heat. A mechanic friend suggested because the injectors were not coded to ECU by mechanic who did engine swap, it built up excess in burnt fuel which built up in dpf and caused it to collapse. Could this be the cause? Also would they usually require coding if changed? Any help on the matter would be greatly appreciated. Thanks in advance.

Zak