Customers are often your adversaries. In fact, it's almost entirely the case - They're looking to extract concessions, get cheaper goods and services, etc. The customer has incentive to bleed as much as they can from the seller, and the seller also has incentive to bleed as much as they can from the customer. Cooperation despite adversarial relationship is the great benefit of capitalism, but doesn't mean you can ignore the adversity.

There's also a very different mode to their relationships. Symantec is selling to the Russian government - bureaucracies, and it's selling black boxes. Russia is trying to leverage it, to give it advantage in a different mode - Intelligence. Both Symantec and the Russian intelligence agencies are in the infosec business. It's not that uncommon for businesses to do business despite competing in some areas - Samsung was a core iPhone supplier despite also making phones.