He's a 9/11 Truther too; of course he can.You can scale up from a single prisoner in a single room to estimate the work involved in killing thousands at one time.
You can do the same with crematoria although it would be more useful to look at how big agriculture disposes of animal carcasses on an industrial scale. How were the remains dealt with during the swine flu or mad cow disease incidents that involved killing all the chickens or all the cows in a country? Were they burned?
You can't simply say that something that sounds implausible is possible because nobody has ever done it before or after.