How can Disk Drill say it has recovered 2.4 TB of files when the HDD is only 2 TB?
It looks like Disk Drill has found the same files multiple times.
For example, here the program says it has found four individual .iso files of  6.36 GB. In reality, the original medium only had one such file. 



This would explain why the total size is several times as large as the original amount of data.