IMing in Awkward Office

BigBoss is my manager's boss. I've worked with him for over 3 years and he's got strange habits. First, he instant messages you with a greeting, like "hi" or your name, but stops there. I used to think this was a summons to his office, so I would dutifully wander over to his office, but its become apparent that BigBoss isn't beckoning you to visit him... so, I respond to BigBoss over IM. But the conversation ends there.

Fast forward an hour. I go to my manager's office. I said, "Hey, does BigBoss IM you about nothing?"

My manager's officemate, Josh, responds first: "No, BigBoss never IMs me."

My manager, Nick, who I've worked with over 3 years too, responds, "What did he want?"

I don't know, obviously, because we only exchanged greetings!

Nick: BigBoss does that to me all the time. I usually go stand outside his office and stare at him through the window.

Me: I can't see through his window, I'm too short to see through the mailbox attached to his window.

Nick: Go crouch and look UNDER the mailbox! Do it now! Peek in his window!

Thanks, Nick, I'll take your advice on how to be super awkward for sure. I caught up with BigBoss at Happy Hour and he said I didn't respond fast enough, so he forgot why he IM'd me.