Creature telepathy and illusions?

I am running a D&D 5e campaign, and we had an interesting case come up in play last night.

The party cast minor illusion to conceal themselves in a cave at the end of a narrow canyon, and then a Spined Devil, with telepathy, spoke to them telepathically (and they replied).

Does the presence of the illusion mean that the Spined Devil could not have known telepathically that they were there?

In other words, since the party had been conversing while within the Spined Devil’s telepathic range, even though he was out of sight and ear shot, would there be any reason to think that he would not be able to ascertain their (general) location despite the illusion, once he arrived at that location?