Other mistake: When Tod has almost finished speaking to Helen after he's told her about his conversation with Gary, her hands are resting on the cooker ring. She had just been frying chicken so these rings should be scalding hot and she wouldn't have been able to rest her hands on them.
Continuity mistake: When Tod has spoken to Gary and tells Helen he is "one messed up little dude", she sighs and her shoulders slump but the very next shot has her hands on the counter edges and she's staring straight ahead.
Answer: If a child becomes estranged from their father after their parents have divorced, it's not all that uncommon for the child to take their mother's maiden surname instead of their father's.
raywest ★