Not quite and not always. My credentials are 30+ years programming and working with both hardware and software. What your dad is most likely referring to is that when a computer is seized in a surprise raid, there is almost NOTHING that a perp can do that will permanently remove data on a computer. If the police are careful, even erase triggering anti-tampering controls can be circumvented. Note that this applies to data stored on magnetic media and static memory devices. Anything that is based on constant power like DRAM is lost when power is off for any length of time.
When the user deletes files with the standard delete function, the data is not really lost until some other data over-writes it and even then really sophisticated operators and software can recover portions of it due to certain physical characteristics of magnetic storage. There is software available that does what is called a 'scrub' of data that you really want gone. Generally it makes multiple passes of the file area laying down as random a pattern of binary bits as can be done. This is what the DoD and other security agencies do when erasing sensitive data from their own computers.
[T]hey print out the records as they come, like a reciept ...
This maybe true on some voting machines but not on the electronic ones that we are using in my Florida County. The data is stored in a 'secure' on-board memory and is also sent (periodically?) to a polling place accumulator where it is sent via modem to the SoE Central Office. If everything works right, at the end of the voting day the poll workers state how many voters they have processed and the counts match to the transmissions and then the on-board memories can be cleared for the following election.
I don't like or completely trust it though and would have preferred a type that is called a 'mark-sense' system where you still actually mark a ballot by adding a mark on it. You then take it to the 'reader' which then checks for any 'over-votes' [remember them?] and if that is OK you get get a paper receipt showing your votes, the marked ballot is saved for a confirmation trail and the vote is tallied through the reader.
My understanding is that many counties here in Florida, faced with replacing the 'Chads', liked the touch screen voting because there were no consumables used that cost money each election. With the mark-sense you use paper and ink but I really like the audit trail!