It may not be commonplace to find competitors partnering with each other, but it is also not a rare case. Besides, such collaboration only lasts for a certain period and is not expected to be done in the long-term.
Checking out your competition
In every industry, competition exists as there will always be various businesses that will offer similar goods and services. Even for industries where monopoly ensues, there are still indirect competitors that can provide alternatives to consumers. When you run a business, you do not operate in isolation, so you also have to be conscious not only of your market but also of other players in the field.