I think so, yes. No borders to indicate the selected tab, no background color. It took me a while to notice the selected tab is likely to be the one with the "close" cross and the 1px thin accent red above it. It is plainly bad. Oh and the text is not bold, just a bit lighter than the other tabs.

> there are competing usability concerns

This is very true, especially since the author uses red and green for ok/cancel buttons. A colorblind colleague of mine actually likes the current trend of grey-ifying stuff because there is an increased difference in luma, not only in chroma, between elements.