It wasn't (and isn't) a law. It's a procedural norm that the Senate follows (except when they don't want to) to make judicial branch nominees need to overcome a filibuster for approval, but it wasn't required. In the past, most judges would get confirmed in the Senate with votes in the 95-0 range. Here's a list of Senate SC confirmations. Many passed with voice votes only (didn't even count). One (Matthews) even got confirmed with a vote of 24-23 (less than half of the total Senate voting at all).

That was, until Mitch McConnell decided he would completely block Barrack Obama's appointments, not just to the Supreme Court, but to any federal court. McConnell blocking all Obama appointees in 2012(ish) led to Harry Reid removing the filibuster "requirement" in 2013 when the Senate made their rules. This back and forth between McConnell and Reid was really an extension from McConnell's time as a staffer I'm the Senate when Nixon was in the White House, which the PBS article talks about. We're just now (in the last decade or so) seeing the effects of things McConnell decided in the 60s. This is gutter politics resulting from the Senate's bullshit rules that allow the minority party to prevent change unless it benefits the rich and powerful.

No, that was for other judicial nominees. McConnell extended it to Supreme Court nominees in 2017 after 2 failed cloture votes on Gorsuch's nomination. Which he obviously wouldn't have done if Hillary won.