It is unlikely but not impossible that an electronic device caused the jet to fail. As the engineer stated we do EMI testing on all products including aircraft, however it has been my observation that this testing does not cover all eventualities and that EMI is poorly understood particularly in aviation circles.
Our firm is currently working with an American contractor who -in 2006- specified pigtails for shielding termination on a military aircraft. EMI is infinitely complex, and if engineers are still failing to make the most basic of EMI decisions correctly, anything is possible.
Trains also require EMI testing to 20V/m. About 10 years ago we worked on a new train running out of NYC which would open the doors and apply emergency breaks when a cell phone was used in just the right location.
Stating that EMI could not cause a flight systems failure is ridiculous. If they feel it necessary they should conduct a review.