Aside from importing external geometry,
At 19:25, you use an alignment constraint to make a B-Spline normal to a line (axis).
Alternatively, you could have selected the endpoint of the B-Spline, the axis and created a perpendicular constraint.
In this simple case, using alignment does the job finely, but if the line (axis) weren't horizontal, then it wouldn't work.
Of course, if you have no line at all, like in the other end of the b-spline, the only possibility you have is the alignment constraint.
If you had imported external geometry, it should be possible to use this perpendicular constraints between endpoints (you select the endpoint of one external, you select the endpoint of the b-spline, you hit perpendicular constraint).
At 22:17, it is a good example of something that happens sometimes, where a sketch that, as it is constrained should not be a broken face and it is. This is a bug that must be unveiled. You check all the intervening elements, including the path. Generally, it is only a problem of the closed profiles that define the cross-section(s). Many times it suffices to just open the sketch, try to drag one single point, that won't move as the sketch is fully constrained. Close the sketch, repeat the sweep. By the way, checking and redoing goes until 24:50, so more than 2 minutes of productivity time lost because of this bug.
Nice to see such video tutorials.