He means the vet 1 sight bonus in cover. He talked about it during his stream. Section behind sandbag on right fuel on rachnaya spotted a grenadier capping the nearby strategic point.
I know what he means but that is not self spotting. Self spotting is the ability of certain units to see (almost) as far as their own weapon range so that they do not need other units to spot for them in order to fire from max range. For example the Command Panther and the Puma both with 50 weapon and 50 sight range, or a Pathfinders recrewed M2HB with 45 weapon range and 50 sight range.
Infantry Sections can not self spot by definition because the maximum range on any of their weapons is 35 which is the same as the standard sight range.
Being able to see further is not self spotting and does not give an as significant advantage. I don't want to start a semantics discussion here but self spotting is a clearly defined and powerful trait and it's important keep that separated from this discussion and stop randomly attributing things to Infantry Sections that aren't true.
They can see quite a bit further at vet 1 when in cover (45) which helps with reconnaissance and which helps to spot for HMGs and ATGs and other vehicles and that is quite powerful. They have it because they are tied to cover more than other mainline infantry and generally can't be as far forwards. Perhaps it can be toned down now. But it's not self spotting and a top player like Orangepest should know the difference.