I earlier posted about the Stranger's αἰδώς (shame or awe) on responding to Socrates' request that he use a vaguely "Socratic" approach to the conversation, with short exchanges rather than long speeches. It is worth noting also that the Stranger’s αἰδώς mirrors Socrates’ own remembered αἰδώς at encountering Parmenides as a young man (Theaetetus 183e6), an encounter that Socrates just recalled (217c5-7).
There, Socrates showed himself as an overconfident young with much to learn yet from a more experienced philosopher. As we learn from the Parmenides (127eff), Socrates thought he could easily refute Zeno's paradoxical arguments about the many and the one by introducing a version of the theory of forms. But the aged Parmenides himself refutes Socrates' arguments, leaving him at a loss. It is this that seems to be the source of Socrates' reverence or awe; not Parmenides' age by itself, but the fact that Parmenides showed him the difficulties with his own position.
Now, the Stranger must have heard of Socrates’ fearsome powers of refutation before meeting him; otherwise his αἰδώς could only be explained as the conventional shame of a younger man upon meeting an older man. This is a possibility, since Theodorus describes him as merely a companion of those around Parmenides and Zeno, not as a companion of Parmenides himself; the Stranger may never have met Parmenides, if we take Theodorus literally. But we are never told that the Stranger is a young man.
At any rate, Socrates appears to the Stranger as a figure inspiring reverence and shame, not someone to be trifled with lightly, especially not by giving oneself airs and putting on exhibitions; we might say that Socrates is to the Stranger as Parmenides was to Socrates. But just as Socrates did not simply bow down before Parmenides’ wisdom (even if he was rendered uncharacteristically at a loss), we should not expect the Stranger do so before Socrates. His very presence is a challenge to Socrates. And yet he seems ashamed of his possible challenge: if he is there to pass judgment on Socrates’ philosophical practice, the presence of a silent Socrates observing him also constitutes a test of the Stranger’s own philosophical activity, including his political thought.