observation: only lahshar and her cadre are mentioned leaving the caravanserai after her argument with bashasa about kai
observation: this exchange happens and kai decides to say That.
Kai tilted his head. He said, "Anything you'd like to say to me?"
Lahshar had been caught by surprise, unprepared to see him, and she obviously hated that. She lifted her chin. "You should remember your purpose here."
"My purpose," Kai said, holding her gaze. "Is what Bashasa says it is."
observation: kai is still lurking standing right outside the room they were in and was able to to hear every word of lahshar and bashasa's conversation
implication: someone in that room would just as easily be able to hear a conversation happening outside
observation: bashasa is present elsewhere in the building almost immediately after this, which suggests he did not leave through the same door as lahshar and instead went further into the caravanserai.
implication: bashasa is still inside aforementioned room when kai confronts lahshar like two metres away from the door
conclusion: bashasa absolutely heard kai say THAT to lahshar .
+ bonus for further consideration, this scene that takes place approximately twenty minutes later:
"I know the depth of your loyalty and commitment to our cause, to..." Bashasa hesitated and shook his head, for once unable to find words. "I would...If you..." [...] Bashasa grimaced. "I should go."
'i know the depth of your loyalty and commitment to our cause . to --' no no what were you going to say bashasa . 'to-' TO WHAT BASHASA?????? TO WHAT??????? 'i would--if you--' YOU WOULD WHAT. TELL ME . TELL ME BASHASA .