SOP (like 99% sure). Many airports have parallel runways with more than enough clearance for two simultaneous landings. I have been a passenger in this scenario at least four times that I can think of, and I don't fly that much. I think those were in Denver, SFO and LAX. I don't recall there being any situation that would be considered an emergency on any of those.

The runways are likely pretty far apart. Telephoto lenses compress depth and make objects appear closer to each other. It's why telephoto lenses are used for portraits to make facial features look more attractive and with slightly less depth.

Looks like San Francisco. There are two main runways there, this is common. I think it's just time and chance to land at the same exact moment like this.

So the Alaska is a e175 which is about 70 people vs the United which is about 170 people. It looks close because of the angle and some camera tricks. Landing on parallel runways happens all the time.

They are called Precission radar monitoring approaches and they start doing them when things get super congested. Requires us to listen to another radio so atc can tell us to break-out if someone crosses the no go zone in between the runways.

I've done this (sitting in a passenger seat), it's normal. This video is a bit of an optical illusion, the planes are nowhere near as close as they look.

There are certain airports where it's standard procedure.

Likely just an issue with the perspective of the video, I bet these planes have plenty distance between them if you were to see them from the front

It looks dangerously close due to the camera lens.

In reality it wasn't.

Not necessarily standard, but not likely an emergency. Loads of places have the setup required for parallel landings / takeoffs, it's just usually more efficient to have them alternating

Here's a list of the places that have parallel runways (bottom of the page)

Captain Joe has a good video on PRM and SOIA approaches.