In the introduction to the Monster Manual (p. 9), the description of telepathy states:
Telepathy is a magical ability that allows a monster to communicate mentally with another creature within a specified range. The contacted creature doesn't need to share a language with the monster to communicate in this way with it, but it must be able to understand at least one language. A creature without telepathy can receive and respond to telepathic messages but can't initiate or terminate a telepathic conversation.
A telepathic monster doesn't need to see a contacted creature and can end the telepathic contact at any time. The contact is broken as soon as the two creatures are no longer within range of each other or if the telepathic monster contacts a different creature within range. A telepathic monster can initiate or terminate a telepathic conversation without using an action, but while the monster is incapacitated, it can't initiate telepathic contact, and any current contact is terminated.
Are these rules intended only to apply to monsters' telepathic abilities?
Specifically, when it says:
A creature without telepathy can receive and respond to telepathic messages but can't initiate or terminate a telepathic conversation.
Does that mean that characters can respond to "a monster's telepathic messages", or "telepathic messages from any source"?
Several Jeremy Crawford rulings seem to imply that the intent is for this to apply only to monster telepathy (see two March 2017 tweets here and here, for example). However, I've seen this cited in arguments that have nothing to do with monster telepathy as well (see this answer to "Is the Warlock's Awakened Mind telepathy two-way, or only one-way?"). So I just want a clear answer as to what case this section of the rules applies to.