James P Ferguson, witness to the assassination

[Rsmyth]

In the trial testimony James P. Ferguson states that in the box was a "gentleman in citizen clothes I did not know." Here he is referring to Rathbone.
In the Lincoln Assassination Encyclopedia by Steers, he says according to William J. Ferguson "Major Henry Rathbone was dressed in civilian clothes, not his military uniform..."
Unless James was accompanied by his brother or father could Steers be mistaken with this statement?