Short Final: Say Altitude

I was on an IFR arrival into Houston a while ago with busy Approach Control, when I heard the following exchange:

Approach Control: "N1234 say altitude."

N1234: "Altitude."

Approach without hesitation and very patiently: "N1234 say the altitude you are flying."

N1234: "Oh, 5,500 feet."

Approach: "Thank you. Altimeter 29.93."