No, that's not all we saw. In the trailer we saw the oath of the peach garden
where supposedly Liu Bei, Zhang Fei and Guan Yu swore to be brothers and die at the same year, month, day and time. However, this is a
fictional event that is described in the medieval fantasy novel "Romance of the Three Kingdoms" and never happened historically, as there is no mention of it in the actual historiography that records the events of China at the game's era (2nd and 3rd century C.E.), which is called "Records of the Three Kingdoms".
https://en.wikipedia.org/wiki/Oath_of_the_Peach_Garden
In the same scene we see the weapons that are described in the fantasy novel for the three heroes, not historical Chinese weapons of the era. For example, Guan Yu (the one in green) is depicted wielding the Green Dragon Crescent Blade, which is a fantasy weapon mentioned in the fantasy version. According to Chinese folklore this weapon was magical, as it was made from pieces of the body of a dead green dragon, hence the name.
https://en.wikipedia.org/wiki/Green_...Crescent_Blade
In reality this is a guandao weapon,
which according to most historians and sources did not exist until the 11th century C.E. In addition, Guan Yu fought mounted, so using a heavy, unwieldy two-handed polearm as his main weapon while riding is highly unlikely.
The trailer also finishes with a
fictional battle (the battle of Hulao Pass) from the fantasy version, in which the
fictional duel of Liu Bei, Zhang Fei and Guan Yu with Lu Bu took place, which is the duel we see at the end. Liu Bei doesn't engage in the trailer, that's why we see a duel of 2 vs 1 and not of 3 vs 1, as described in the fantasy novel.
https://en.wikipedia.org/wiki/Battle_of_Hulao_Pass
I would say that judging by what we've seen and generally know so far, we already have pretty solid evidence that this is the fantasy version, not the historical one. Unless of course the team responsible of the marketing trailers messed up so royally and made a totally misrepresenting trailer, but I find that highly unlikely.