B.W. didn't predict that Russia would defeat Ukraine in days, but he did draw comparisons to the second US invasion of Iraq, implying that it would take about three weeks for Kyiv to fall (about the same time that it took the US to capture Baghdad).
However, note that in the year prior to Putin's invasion, the US had already given $650 million of military assistance to Ukraine, and for years had provided considerable "intangible" support in terms of military training provided through the US National Guard. Ukraine's success may have surprised a lot of people, but it reflects favorably on Ukraine's longtime relationship with the US military, going back to the 1990's.
For information about US military support over the previous year, see for instance
For information about longtime US National Guard involvement, see this article, which looks at the California National Guard's relationship with Ukraine, although I know that Florida NG has had a similar ongoing relation.