The title doesn't fully do justice to how unfair it was to you

1.) Not just dubs but 8player-dubs, which is a whole different ballgame.
2.) The fact that they wanted to choose a random partner for you.
That said at least they're not inviting cooks. If it had been a 4player dubs game and I got teamed up with some random person of your rank, i'd check if you have dubs medals. If you have say silver/gold I'd accept. For me the deal falls on the 8-player part of the equation.
A quick look at the people they invited show that 3/5 have decent teamgame exp... so at least they're not being selective that way, that would be far worse imo.
tldr version; Totally within your right to decline, get on with your day and forget about these jokers
