"We pay for your Russian mobile OS, you buy our Chinese stocks, win-win", probably as simple as that. Although normal Sailfish is probably almost the same as the Russian fork, there is more to gain from a partnership where the partner can also invest in 'them' (whether that's Huawei itself or Chinese activities in general), especially considering that the meeting (logically) also explicitly discussed economic cooperation in other fields. It's all fine as long as the improvements to Aurora OS trickle back to Sailfish OS.