Actually, to be the bearer of bad news, if you're talking about the Ryzen 2700 on your account, you only have 8 physical cores. The other 8 threads are logical. There are many threads on this forum about this discrepancy and how to get the most out of such a system. Search for "hyperthreading".
Regardless of that, to address the matter at hand, I don't think it is actually doing both at the same time, but rather switching between the two units. This happens a lot when you have mixed long (e.g. Woodall) and short (e.g. PPS) tasks. When you get near the end of a task, Boinc downloads a new one, but when they are vastly different sizes, it starts to switch back and forth because of a) different deadline setups and b) weird logic, until the first finally finishes.
Or, I could be off base. Can you take a screenshot of your Boinc window showing both tasks?
Eating more cheese on Thursdays.