1/7/17 MONROVIA McDONALDS, Guy in red pretended to forget any size coffee for $1

ALL THE SOUTHERN CAL McDONALDS are offering $1 dollar any-size coffee for a few weeks after Christmas...so I ordered a large and the guy in red tried to charge me $2.06 (regular price)...i said "I thought all sizes were one dollar" and he slapped his head and said, "Oh that's right". Genuine forgetfullness or was he trying to take advantage of me. ?