Can negative answers equal stealing?

If someone gets a negative answer to a question involving a purchase at a store, is it stealing?

Today, I was grading the tests I gave last week covering linear systems in Algebra. I was actually quite impressed with the majority of students who were successfully solving the mixture, distant, and linear systems questions. Then I came across an answer where the student answered with a negative value to the following question:

Mr. Stadel bought a total of 31 Red Bull drinks. Each individual can is priced at $2 and a 4-pack of Red Bull drinks is priced at $7. Mr. Stadel paid a total of $56 for the energy drinks. How many individual cans did he purchase? How many 4-packs did he purchase?

The student answered -6 for the amount of 4-packs. Checking their work, they accidentally forgot to account for a negative in their solving. Of course this prompts me to encourage my students to analyze their answers even better, considering the practicality of their answer before submitting it...

or maybe -6 meant I stole the Red Bulls.