Your crush may come into class sighing very obnoxiously every morning because he may be trying to get someone in particular to notice him.
Perhaps he hopes this person will use the fact that he is sighing as a conversation starter at some point during the class or afterward.
Thereby, yes, he may be trying to get someone’s attention.
This is especially true if you notice that when he obnoxiously sighs, he consistently looks at the same direction in class.
If his head is constantly drawn to the same direction whenever he comes into class and sighs, there is a good chance that the person that he is hoping to catch the attention of is positioned in that general direction.
Yes, he may need someone to talk to.
However, he most likely would prefer it if the person that he directs his obnoxious sighs to, takes the initiative in starting a conversation with him.