I've looked through a number of articles on this issue and haven't been able to come up with more information on the actual wording of the resolution, but everything points to limiting the ability of formula manufacturers to promote their product, particularly where it is promoted as superior to breastfeeding.
When the HHS spokesperson said the resolution "placed unnecessary hurdles for mothers seeking to provide nutrition to their children" it looks like that was a bit of a stretch. There is no indication that mothers who could not breastfeed would be restricted from buying formula. It's possible that less retailers would carry formula and prices would rise if it became less popular, but that's the free market at work. So unless the WHO, a number of physicians who have come out against the US tactic, and every news outlet reporting on this story is being dishonest about what was actually in the resolution, the US was bullying Ecuador in support of formula manufacturers.
Even if there was a legitimate reason to oppose the resolution, this whole ordeal makes the US look bad every step of the way. Bullying a smaller country to change their laws, that doesn't look good on the world stage. Backing down when Russia steps in, that just makes it embarrassing.