When you erase a file by dragging it to the Trash and emptying that is simply deletes the entry from the Directory: the file still exist but as the computer has no record of it it can be over-written. If you dragged your Home Folder to the Trash the same wouod apply.
To erase a disk completely you use Disk Utility to erase and format it - formatting lays out the sectors which the system will use to allocate your data. Pre Catalina this also erased the system, leaving a completely empty disk, so you would have to re-install the system. In Catalina the system is on a separate sector which you can't touch so it remains in place.
Since you said you 'erased the disk I assume you did the latter. This process over-writes the previous contents of the disk. For a more secure erase it can over-write it many times. All this can sometimes leave tiny traces of the original data, but pretty well only the FBI could retrieve anything at all: you don't need to worry about that as you are not a terrorist (presumably).