This tweet came from ZTE's UK account, and it seems they are really excited about some of their smartphones that will be announced in 6 days, and will be the "most advanced gaming smartphones". It's hard to speculate what exactly this means, but there are a few paths they could've taken.
The first one would be making phones similar to the Xperia Play. If they are talking hardware here, than that is probably one of the options, as hardware buttons can offer a much better gaming experience than touch buttons, which can often lead to a frustrating experience when playing a game.
The second option could be referring to the processor, if they are using something like Tegra 3, which has more exclusive and nicer looking games for it, but that wouldn't exactly be a unique thing in the market right now, with multiple phones using Tegra 3.
The third option could be referring to software. ZTE could have obtained a license from Sony for their Playstation Mobile suite, which means that their phones would run PSX/PS Vita games. It's also possible they could be doing all of the above, and really push the envelope on what a gaming device can do. But we won't really know until next week.