I think he was surprised that Char was in contact with the professor, everyone has been very suspicious of her.
Sure, but how did she show up in the conversation then?
The monitor popped up between pages 8+9 and wasn't around until then, so either
-Haruto just made the monitor at that point, in which case he shouldn't be surprised that Char chimed into the discussion (since he would have made the monitor so that she could chime in), and her saying "Yes, thank you!" shouldn't be enough to have him be shocked at the content of what she was saying
-or Char has some way of activating the monitor herself, which would be something I just don't remember happening, hence asking about it
Just seems like a bit of a weird interaction from what I remember of how his barrier stuff is supposed to work. Unless we're just supposed to assume the monitor was there the entire time and the author just didn't draw it until then for whatever reason.