It's a spectrum. Possible difference include copyright ownership of the work, applicability of the work directly to the business's goals, the reusability of the work as part of your portfolio...
...but if you're building something on a company's API to specifically get hired by them, it's effectively an unpaid internship, regardless of the license and the copyright.
...but if you're building something on a company's API to specifically get hired by them, it's effectively an unpaid internship, regardless of the license and the copyright.