The example mybot.c looks very clean and simple, nice project.
It's been a while since I played with telegram bots, but I remember thinking it is one of the best APIs I've used. So simple to register a bot directly through the chat interface with the not father, and a 5 second job to add message posting to a bash script etc.
By comparison I am currently doing some work with Google Chat of all things. If your bot is in a Space (channel/grouo) it only gets webhooks when someone @-mentions it. Which is really not ideal if you are trying to have an assistant bot participate organically in the convo..
I poked around with doing a Slack bot recently and the hoops for an app were many and confusing. Not Google credentials level but more than I cared for.
I've used both Discord's bot API as well, and can say it was way more convoluted to get up and going. Telegram's API was a joy to build in. This was in Node.js.
You need to use the "Telegram API": https://core.telegram.org/api#telegram-api (not the "Bot API") to develop your client. It uses MTProto to communicate with the server, so I suggest you just use a library that supports it like Telethon if you want to program in Python.
It's been a while since I played with telegram bots, but I remember thinking it is one of the best APIs I've used. So simple to register a bot directly through the chat interface with the not father, and a 5 second job to add message posting to a bash script etc.