[naveensky]

one another scenario is that if you open the domain from browser, they will do 301 redirect, but for traffic coming from Google/search engine, they will show their actual content.

[maltelandwehr]

If this is done with SEO in mind, at first they will also do a redirect for Google Bot.

Then they build links to their domains. Once it has more backlinks than the real domain, the redirect is removed.