The above links is perfectly LEGAL, so you're fine as long as you purchased a legal key for the install disc.
Not sure what happened with that rep but it sounds like he doesn't know what he's talking about.
*My advice is just buy an official disc online. It's $128 from some stores->
http://pcpartpicker.com/part/microsoft-os-fqc06950
You can get the non-Pro version for as low as $90 after rebate so make sure you would benefit from the Pro version anyway.
Other:
An alternative is to use Windows 10 Technical Preview. It's not nearly as stable, but it may work just fine for you and it's free for now.