As he seems to becoming more anxious about his speech Matthew has been referred to the therapist.
As children become more self-aware this sometimes happens, particularly as the transfer to secondary school will take place shortly with all its challenges.
Matthew talks in the video clip about his concern that the other children should not know that he is being observed and chooses to construe the speech and language therapist's visit as a means of helping the teacher. It is important to respect the individual child's feelings and talk with him to allay any concerns.
Generally, younger children may want to show off their connection with the visitor, and will tell all their friends that they know you. Older children, like Matthew in Year 6, are more likely to prefer their relationship with the therapist not to be acknowledged, so that the other pupils do not see him as different.