This app is a messenger and thus has to connect to the internet to send and receive messages. The content of each message is only tranferred encrypted. The server the messages are send to has no way of decrypting any messages in a reasonable amount of time because there are no cleartext keys stored on the server.
The only type of key stored on the server are chat keys in handshakes. Those are encrypted with a user's key which is never transferred at all so the server also has no way to decrypt those chat keys.
Since users can set their own server in the settings, the developers of the app can't make any statement regarding the transport layer encryption used to connect to the server.
Aside from that, this app does not connect to the internet or collect any data on it's own.