The requirement in the statute isn't just that he committed treason, actually. The loss of citizenship from committing treason doesn't actually occur until the conviction for treason. And conviction for treason is both statutorily and constitutionally impossible unless you have two witnesses testify to the commission of the same overt act, or unlesss you have a confession in open court. This was a very intentional protection by the founding fathers based on prior abuses of treason laws in England.

So, even if he absolutely did commit treason, he is a citizen unless the prosecution both occurs and achieves all of that. Citizens deserve due process, period, since government conclusions and criminal charges can both be wrong, and loss of life is a very severe thing to make a mistake about.