It does not use OP_DROP as that would make the tx non standard. The public key is simply the ASCII message. Look at the last output and hex decode 4d6573736167653a205468616e6b20596f7520466f722054686520427567205265706f7274202d2 07069756b. Messages exceeding 120 bytes will be added in an additional outputs.
Oh god, thats awful...that is quite possibly the worst way to implement messages in terms of network load...