Riya thinks she is marryings Shivam.
Sarla wants Riya to marry Amit.
Sarla is smart to only use "my son" in front of Riya whenever she wants to refer to Amit.
& By "my son" Riya always assumes it is Shivam sarla is referring to.
Sarla asks Riya - Has your father met "my son"
& Riya replies - Yes, dad has met Shivam.
The day Riya introduces Shivam to her dad, she does say his name is "Shivam".
In front of Riya's dad, Sarla used Amit's name clearly when talking about the marriage (right in today's episode).
Yet, Mr. Mathur (Riya's dad) doesn't think anything amiss!
Who does Mathur think Riya is marrying? Clearly Amit. Because Sarla mentioned it twice to him in today's episode, unless he wasn't paying attention! Though he has met Shivam, and was impressed by him, doesn't look like he remembers Shivam's name. But how did he assume the boy he met is Sarla's son? Seriously Mathur has no clue and he is going on with this marriage without proper details.
From Riya's side she does say - "Even Shivam works at my office" to convey that it is Shivam she is interested in.
Sarla uses her misinformed assumption to her advantage.
But Mr Mathur being a father doesn't really know who is who!
Sarla doesn't even know how much Mathur knows except that Mathur has met Shivam & might not have ever seen Amit.