Cans of paint

A man knocks on his neighbor's door:

"Hi. I noticed you painted your bedroom last month and since we have a similar house, I thought I'd ask you how many cans of paint you bought."

"Sure thing! We bought seven cans"

"Awesome, thanks!"

A few days later, the man knocks on his neighbor's door again, looking a bit ticked.

"Hello again, what's up?"

"Well, the other day, you told me you bought seven cans of paint for your bedroom, right?"

"Right"

"Well, the whole room is painted and we have three cans left".

"Oh, you too?"