I'd bet it is a typo stating ddr5, not on the CPU model. 8GB sticks of ddr5 are rare enough to find as singles, and 4gb sticks basically don't exist - makes more sense if it is a DDR3 system. Plus, the GT 730 is basically only barely a graphics card, a lot of them are Fermi based chips (like gt 400 series from 2010)... They are dirt cheap video output for a machine that otherwise wouldn't have any video out, but they get packaged by less than honest companies/people with other old hardware and marketed as "gaming computers" all the time unfortunately.
Ubuntu is not the limiting factor to this machine gaming, unfortunately. It is going to be choking itself on basically any games from the last 10 years :(