I'm not saying it's proof. I'm saying it's just one piece of evidence. One irregular data point to put on the pile along with the irregular midnight spikes just after they sent people home so that ballots can be counted in secret.
Every single one of these data points are easily explainable through absolutely mundane means, and was usually predicted through these mundane means months or even years in advance.
Why did down ballot dems underperform? Obama hollowed out the state parties to focus the Democrat machine on the presidential elections, with the Democrat party drifting out of touch with the voting base, they're going to lose more and more voteshare to Republicans, a trend that has been happening since 2010 since Obama fucked it all up. This is further shown by the degree to which the down ballot dems compared to each other, namely that progressive candidates outperformed their centrist counterparts, and some of the centrists who lost harder than others were poor campaigners.
Meanwhile the dems billed this election as "stop Trump", so people voted to stop Trump, but that gives no reason or incentive to vote down ballot and lo and behold, down ballot suffered. This anomaly was absolutely predictable by everyone except the blue MAGA crowd shouting VBNMW. There's no real reason to believe something shady happened when there was massively increased turnout, the Republican presidential candidate had been painted as exceptional by both sides, and the Democrats have been on a decade long losing streak with 2018 being the anomaly.