Mix it up?

This morning I made Rich a sandwich to bring for lunch.He's pretty much a potato chip kind of guy but I asked him if he would like tortilla chips with his lunch instead of potato chips. He said,"Ya,mix it up." I grabbed a Ziploc bag and threw in some tortilla chips and then some of his favorite potato chips. I left everything on the counter for him to pack and I went in our bedroom to check my email.

A few minutes later,Rich entered the bedroom holding the bag of chips.
"What kind of chips are these?"he asked curiously.
"Tortilla chips and potato chips,"I replied.
He gave me his head shake and squinty eye look that asks,"Why?"as he held out the offensive bag for me to look at.
"Well, you said to mix it up so I did;a little bit of tortilla chips and a little bit of potato chips." I looked at him wondering what the heck his problem was.
"When I said mix it up I meant ya,change it up.I'll have tortilla chips instead of potato chips today. I didn't mean mix them up together."

He left the room with a huff and a puff and an eye roll. I heard him changing the chips around before he packed his lunch up.Once again I marveled at the realization that Rich and I speak a totally different language.

What would you have done if you were in my situation? What would you think mix it up meant?