Telegram bot is a system software installed within telegram app, I don't see anything making it a scam. Rather those who are using it for their own fraudulent investments are the ones abusing the system. Majority of the telegram group promising to reward you with reasonable amount of crtpto like 'BTC, ETH, LTC don't give out, only 1/10 of them does. It doesn't mean that every one using telegram to promote their crypto coin is promoting scam project, no. Their are some legit ones, but due to scam going around telegram through the abuse of the robot system, you don't know any one to trust again.
To know about a project that is legit, you need to seek for their official project website, try to make several reviews about it, go to YouTube, Google and ask alot of questions about the project that is being promoted by a given crypto company via telegram. And also, try your best too, to get a conversation with the Admin of the project, ask him questions about the coin project he or she has at hand, such should give you a clear view about what's expected from the project. Then from there, you'll decide to proceed with them or not.