A learner can be tired from a conversation that felt easy to everyone else.

A conversation in an unfamiliar language runs on constant effort that nobody else in the room can see: listening, translating, assembling a reply, monitoring your own accent. Twenty minutes of that costs what an hour of ordinary talk would. The tiredness afterwards then gets read as unfriendliness or lack of interest. What looks like withdrawal is often somebody who has spent everything they had.

Give a learner breaks and quieter corners, and treat leaving early as normal. Slow down rather than raising your voice, and let the silences run long enough for a sentence to be built.