tl;dr - It seems like Twetch uses their own proprietary database to index and store transactions as opposed to scraping directly from the chain.
Twetch uses the B:// protocol spec to organize their OP_RETURN data. Here is an example:
However, even if you were to format a custom script with valid parameters and post it on-chain, Twetch wouldn’t pick it up since the data is not picked up by their servers directly through the web app, thus, the TXID is not indexed.
From Klimenos’ blog:
“For instance, using those applications, it is possible to post a message on the blockchain using the protocol requirements imposed by Twetch and Weiblock. However, if those platforms are not aware of the transaction, they will not pull them because they are currently not designed with a mechanism that automatically fetch third-party published content from the blockchain. The opposite is also true: it is possible to post content on Twetch and Weiblock without requiring you to broadcast content to the blockchain in the first place.”