When you state the measurements of an object, you use the expressions "wide", "high/tall", and "long" to refer to the width, height, and length respectively. e.g. The table is 30cm wide, 50cm long, and 40cm high. We do this with every unit of measurement including feet, inches, metres, and centimetres. It's unlikely that any person is really 7 feet wide. It's a humorous way of saying that the person is fat.

Referring to someone's width in feet is a rude joke used to call someone fat. They are saying that person A's stomach is wider than they are tall. Usually feet would just be used in the context of height when referring to a person (or the body parts).

Hi Jenny A foot is a measure of height here in England. It is equivalent to 12 inches. 1 inch = 2.54 centimetres. So the person is saying that the other person is 84 inches wide (7 x 12).