I think they should have gotten someone who has experience testifying in both areas. It was dangerous to call a guy who has not been to the plate before. There are so many firms around, how did they land with this guy?
One thing to think about (it may not work the same in criminal stuff), is that if you have an expert who agrees with you, you list them as a testifying expert. If you talk to one who does not agree with you, you consider them a consulting expert and don't list/mention them at all. Perhaps this guy who took the stand wasn't the only expert talked to, just the one who seemed most helpful.