Are they using some implementation of the Ethereum light client protocol? Last time I checked it wasn't available yet: https://github.com/ethereum/wiki/wiki/Light-client-protocol If they are using the standard protocol then how do they connect to the Ethereum network? Do they use their servers as proxy to the network? Because if it's so, that would defeat the whole point to me.
No, they're not using the Light Client yet for that very reason, but easily could in the future. But in any case, no crypto wallets are light clients. All Bitcoin wallets, for example, use servers because it's impossible to do Bitcoin light clients (at least, they haven't found a solution yet). This app is more about having WeChat with crypto payments and with app interactions. Light client could come later though.
This is totally false. So called SPV clients have been available since 2011 I think. Where the hell did you get this information? Just curious.
Examples of lite bitcoin clients include (but not limited to) breadwallet, bitcoin wallet for android (Schildbach), multibit, bittiraha-walletd etc.