They were probably expecting base64 encoded binary data. Base64-encoded-binary-inside-Base64-encoded-JSON-inside-JSON is a really strange construction if you haven't encountered it before, because of how much space it's wasting playing a game of Russian nesting dolls.
Base64 isn't encryption. The overhead added follows an extremely predictable pattern. That said I've no idea what the performance of common compression algorithms might be in such a use case. The comment was entirely tongue in cheek.
