This being Quirrell, while his reaction may indicate shock, it is also exactly how he would react if he did not have the artefact and/or believed it to be worthless in any case. There isn't enough information there to make any assumptions either way.

Also, in Chapter 90, Quirrell visibly fails to refute Harry's assumption:

"What of the Resurrection Stone of Cadmus Peverell, if it could be obtained for you?"

The boy shook his head. "I don't want an illusion of Hermione drawn from my memories. I want her to be able to live her life -" the boy's voice cracked. "I haven't decided yet on an object-level angle of attack. If I have to brute-force the problem by acquiring enough power and knowledge to just make it happen, I will."

Another pause.

"And to go about that," the man in the corner said, "you will use your favorite tool, science."