According to Wikipedia you’ve been told correctly. Lurchers are sight hounds mixed with another breed type. I had the impression ‘Lurcher’ is an old term for sight hounds but seems it’s more complicated. I’ve heard it used for New Zealand pig dogs. They tend to have a lot of greyhound type sight hound in them but it’s hard to say exactly. Like working farm dogs they’re bred for working ability, and not necessarily line bred.
Either way I’m working on a project to do with New Zealand stock herding dogs, not hunting dogs. So I’m not an expert on lurchers as such. I just read a lot about breeds and working dogs for my lit review.