At least for its Las Vegas segment, it may qualify.

According to https://en.wikipedia.org/wiki/High-speed_rail :

  While there is no single standard that applies worldwide, lines built to handle 
  speeds above 250 km/h (155 mph) or upgraded lines in excess of 200 km/h (124 
  mph) are widely considered to be high-speed.

From https://www.hsrail.org/brightline-west/ :

  Brightline West is ready to connect Las Vegas and the Los Angeles area at speeds of up to 180 mph.

It operates at 200kph/125mph for part of the route, which is the traditional definition (e.g. it's what you see on those maps of European high speed rail). It's barely over the line, but it qualifies.