I think the answer to this is no, bots can not post to other bots directly, but thought it was worth asking if there is anyway to do this indirectly like through a group chat?
I tried to setup a group in Telegram with one user account and two bots. The bots are linked to Node-Red using the contrib-telegrambot nodes. When either of the bots sends a message the user group receives the message, and when the user makes a post both bots receive the message. But it looks like there is no way for one bot to receive the message of the other bot when posted in the group, at least now way I have figured out.
As a follow on question, is there anyway to do an inverse echo, by this I mean in the examples it shows a message received, then Node-Red echos the message back to the user. Can you have the echo around the other way, where the bot sends a message and has the same message echoed back (as a kind of confirmation the message was delivered). I think the answer to this is no as well, as it is a bot talking to itself.