The answer to this question is both yes and no.

The Plugable UGA-HDMI-2S can support up to 4K 30hz on only one HDMI port.

When looking at the UGA-HDMI-2S with the Plugable logo on top (As pictured below), the HDMI port on the right will allow up to 4K 30hz. The HDMI port on the left will only allow up to 1080p 60hz.