My workflow is often to open links in a new tab via a "middle click". I will then switch to the tab (usually manually), and have a look at it. If it is not what I was hoping for, often I will gesture "back" out of habit, but this will not do anything, since I opened the link in a new tab.
Posing as an idea - should the "back" gesture on a newly opened tab (i.e. currently visible tab is the oldest in the history stack) close the tab? This could create a risk of an unintuitive scenario where gesturing "forward" won't restore that, since it would be the "forward" gesture on the previously opened tab, which might be "nothing", or could be another tab.
On the other hand, in defence of the idea, I imagine a lot of people will open a series of new tabs, then go through them triaging them for relevance, closing the irrelevant ones. Gesturing "back" on them would seem to be intuitive, and this is likely the expected outcome for the user, if they swipe back on it - if they and just opened it regularly, back would take them back to the previous page, so this should adhere to "principle of least astonishment".