How so? I've volunteered to help run elections in two states in the US, and they both used optical-scan paper ballots. In both jurisdictions, the voter is the one who feeds their ballot into the scanner machine ("ballot box") to be counted. The machine makes a digital copy of each ballot and stores it in local memory. At the end of the night, we then report the number of ballots in the box and compare it to the number of ballots we issued out and the number of people who checked in at the registration desk. We call these numbers in, and the precinct chief hand-delivers the paper ballots, digital scans, and seal records to the county for legal and archival purposes.

In order to manipulate this, you would need the entire polling place staff to be in on the conspiracy, and they would need to cook up numbers and ballots that all match. All to mess with an election at a precinct with no more than ~1500 registered voters. Where those voters are likely of the same political persuasion as the poll workers themselves. High cost, low reward.

To manipulate digital votes you only need to hack one piece of software or bribe/social engineer someone involved close enough with it.

To manipulate paper votes you need to have presence in enough voting booths and influence the votes there.

With paper it might be easier to sneak in a handful of fraudulous votes, but it will be near impossible to commit fraud at a scale that influences the elections. With software it is harder to get that access (although the article shows that one mistake by a dev can make getting access a matter of one hour...), but much easier to then commit election influencing fraud.

The fact that you do not recall any fraud either means it didn't happen (let's hope for the best) or didn't get detected. The latter is obviously very scary.

There's btw more problems with online voting specifically. It's impossible to guarantee the secret of voting. This is not an issue when voting electronically in voting booths.