OK, I'll bite. What is the yawning semantic gap between "pick up" and "connect"? When I read the piece, I understood that one can board the airport express using one of the stations on line 10. (After a bit of a subterranean hike.) I have, in fact, done so a number of times. Subway personnel did not seem to give a flying fornication whether I was picking up, connecting, or simply boarding.
I don't have an issue with the word "pick up" although it is a bit unusual. The article states: "Line 10's airport service starts at Dongzhimen Station and connects to Sanyuanqiao Station where passengers pick up the Capital Airport Express train."
This is incorrect because 1. Line 10 does not have airport service; 2. Line 10 does not go to Dongzhimen; 3. Passengers who take the Capital Airport Express from Dongzhimen toward the airport do not switch trains at Sanyuanqiao (or in the other direction).
There is a station on Line 10 (Sanyuanqiao) where you can get on the Capital Airport Express, as you mentioned. The Capital Airport Express and Line 10 are separate subway lines. The information in the article is not related to Line 10. You can look at a subway map for more information about the Beijing Subway lines if it's not clear.
'Pick up' is millenial-speak for 'catch'.