LG G5 Dual Sim Card

I thought the LG G5 has a dual sim card slot. Meaning I could keep my American SIM card and Korean SIM card in at the same time. Plus I have a micro SD card I want in my phone at all times. But the technician said I can't have both SIM cards in my phone at the same time because it will interfere with the signal. Additionally, even if I could use 2 SIM cards at once it doesn't seem possible to fit my Micro SD card in the slot provided my LG.
Need help ~

where did u get ur G5? is it carrier locked? I think US variant only has 1 sim