This is usually due to caching proxies being employed either on the recipient end by its ISP or the corporation your recipient is employed at, or by some VPN providers (if that's how the email was accessed), all either trying to save on bandwidth requirements, or otherwise control access to contents.
There are many such products available and solve various aspects of accessing contents on the Internet, so I won't be boring you with details. But they can be considered man in the middle type appliances, and go from mildly annoying to disturbingly alarming in ways they're employed. So even though I can't give any opinion whether this is due to something legit or illegit (your question is rather vague, so speculating on true reasons behind this happening is rather impossible), if such caching proxies are used, that would explain double recipients at the same time but in different geographic locations.
Best course of action would be to notify the intended recipient of your email through other channels, if you have reasons to suspect the latter to be the case and see what they make of it.