Since the Content Distributed Network (CDN) is not handled by Telegram itself, the owners may tamper these files. Telegram sends their sha256 sum for clients to implement this additional verification step, which now the library has. If any CDN has altered the file you're trying to download, CdnFileTamperedError will be raised to let you know.
Besides this. TLObject.stringify() was showing bytes as lists (now fixed) and RPC errors are reported by default:
In an attempt to help everyone who works with the Telegram API, Telethon will by default report all Remote Procedure Call errors to PWRTelegram, a public database anyone can query, made by Daniil. All the information sent is a GET request with the error code, error message and method used.
If you still would like to opt out, simply set client.session.report_errors = False to disable this feature. However Daniil would really thank you if you helped him (and everyone) by keeping it on!