Author POV,

As soon as the professor looked at Emma, he was quite surprised as James was standing with her..

Emma started staring at the professor at that time and seeing him staring at him, James looked at Emma with his slanted eye..

So, James has no doubts..so Emma started to be normal ..and tried to ignore the Mr. Johnson as much as possible...

So James didn't say too much and didn't make any strange behavior seeing the professor in front of him..Because somewhere he didn't want Emma to doubt him at all Or if Emma finds out that James knows him, so...he tries to take Emma away from him...