followup question - isn't that just a load of bull?

how foreign the Civil War was to European generals given the numerous advancements made in the Civil War like telegrams, repeating rifles, and trench warfare

telegrams were already used already in Crimea at the very least weren't they?

let alone trenches, a staple of warfare for centuries...

If anything they saw them as over eager amateurs.

One of the reasons the French and British wished for US divisions to be placed into the existing command structures was to ease the transition to modern warfare. But political pressure from Wilson ensured the AEF remained whole. But what that did mean was that as US units arrived in France and before they were ready for combat they spent sometimes several weeks behind the lines at schools set up by the French Army training in things like practice raids, using gas masks, constructing fortifications, and trying to benefit from their allies knowledge. The French also provided a large amount of the modern weapons to the AEF, from machine guns, to tanks, to aircraft many were given over in France, more were produced under license, until US designs were in production.

The USN also sent a division of battleships to Scapa Flow to operate with the Grand Fleet. And while they were welcomed as friends and their presence greatly appreciated as it meant less strain on the RN, they were not up to snuff yet. It took months of training to get their gunnery good enough to be relied upon, and you had all the minor frictions and in the moment mistakes initially from two different nations operating together, but by the end the US ships and commander shad adapted well to the British fleet's standards.

The US fought in the Spanish American War in 1898 which was against Spain who at the time was considered a Major power. It wasn't until after its defeat that Spain was no longer considered a great power as the United States took its place. So the entire premise of the question is flawed.

Could you link the video in question please? Might help add some context.

Trenches were certainly nothing new. Armies had used them for centuries, even against the bow and arrow. Perhaps a good precursor was during the US civil war the South dug in as Grant approached Richmond. There was even an effort to tunnel under the Confederate lines and plant explosives. Something done on both the Western front and in Turkey.

Military Heritage magazine (I no longer have the issue) had an article of one of the wars between Russia and Japan in early 1900. It started when Japan broke off ties and sent it's fleet in to launch a surprise torpedo attack against the Russian Navy (and you thought it was just Pearl Harbor). Russia had been preparing for war but, had a lot of corruption in the government and the military was widly scattered. Some of the cities the Japanese attacked very much showed what was going to happen in WWI. Machine guns, barb wire, fast firing artillery, high body counts. This happened in several battle areas around the globe.

But, as to the original question I think many French and British officers had their doubts about the Americans but, I don't think the German Command had any.
One of the reasons they wanted peace with Russia was so they could move all the Eastern troops to the Western front and hopefully attack and defeat the French/British at least get a peace treaty with them before the Americans landed.

Follow up question: in a history class a while ago we were looking at WW1 and i remember a quote by the american commander. It went something like 'If another person asks me if the Americans will really fight, I shall be quite cross.'

Is there any truth to this?