I think Sid is more relaxed also because he saw how Sana is with her brother. Laughing and she fell on the floor. Shehbaaz ke haath mein cake nahi hota toh pura chadd jaati jhappiyan pappiyaan. That makes him feel better about how she generally behaves. That means thats just how she shows love specially to someone she has been missing or has been wanting to meet. And seeing Sana-Shehbaaz bond makes him more relaxed coz Shehbaaz is chill too.