The Russo-Japanese War infantry of 1905 you mean. The correct year on your video title.
I believe his original post was "Russo-Japanese War era infantry and soldiers of 1915" - two different groups, if I remember the rules about English Conjunctives correctly.
And to answer the original question, up until 1914 ALL armies' infantry were still primarily riflemen with bolt-action magazine-fed smokeless powder rifles and a relatively very small number of machineguns in support.
By 1916, and especially by 1917 - 1918, the civs fighting WWI had added many, many more machineguns to their infantry companies, battalions, regiments and divisions and were adding medium and heavy 'trench' mortars (indirect fire explosive direct support under the infantry's direct control) to their infantry units.
It has been remarked by several academics researching the effects of World War One (Corum, Citino) that the infantry of 1918 was almost completely different in their appearance (uniforms, helmets), tactics, and weaponry from that of 1914, not even considering the massive changes to the Armies in the amount and efficiency of artillery support and new weapons like ground-attack aviation and tanks.
Consequently, to gather all the various questions and considerations, if Civ VII were to divide up the Unit Mix into Riflemen and 'Shock' or 20th century infantry, I would put the dividing line at 1916 give or take a few years, and the Rifleman graphic would be the late 19th century in 'semi-dull' uniforms including, say, the Russian and Japanese white, French red and blue, US dark blue and khaki - not quite as colorful as the previous fusiliers or Napoleonic infantry of the 18th century, but not yet trying to be as invisible as massed firepower forced them to be after 1915.
The initial factors of the Infantry would be only marginally better than the Rifleman (the rifles are a little better and faster firing than previous breechloaders and each battalion has 2 - 4 machineguns added), but they could very quickly be Upgraded with Machinegun Companies, squad automatic weapons (by 1918 Everybody had them), light and medium Mortars, and even Infantry Guns - very light and short-ranged 37mm to 75mm 'pack' weapons for direct support.
Even without any change to the basic rifle, the Infantry firepower man for man more than doubles in the 20 years after 1915 with all the potential Upgrades to the individual Units.