App gets in commandline parameter "-psn_0_nnnnnn", why I installed an app which is compatible with OSX 10.10, on 10.8 app shows warning about incorrect parameter:

-psn_0_176171

Why app shows this? it is installed from Dmg file, it's .app file - on desktop.
Pre to OSX 10.9 apps launced in GUI had a -psn parameter passed to them. This was a Carbon system feature.

From this SO answer some documentation is in Apple's ProcessSerialNumber section of the Carbon Process Manager Reference. This is now marked as a retired document and the methods are noted as removed in OS X 10.9 

Thus in 10.8 there is a -psn argument passed on the command line and the app then sees this and seems to be confused. I would note a couple of other things a 10.10 app will make calls to functions not in 10.8 so your app will likely crash later, also I suspect the app is reading the command line and this is not the best was as noted in the first link in in the comment by  Graham Miln