They wanted to leave.
How many non-capitalist choices did they have?
Two, presumably, since they left one workers' paradise and traveled through another one to get to that embassy fence. What's your argument? That your mom can't have freely chosen to have sex with your dad, because nobody offered her Robert Redford, so your dad's a rapist?
The argument is that running away from something towards an unknown is not choosing the unknown. It is choosing to run away from something that is not liked.
You are claiming because the woman did not chose this one man it is because she was in love with Robert Redford, despite knowing nothing about him.
Um, no, I'm claiming nothing of the sort, which you'd have been able to figure out for yourself if you'd read as far as the question mark at the end of my sentence. I was asking you to explain yourself. Your position appeared to be that since neither hunting and gathering nor having all their economic needs taken care of for them by magic unicorns barfing rainbows were among the East Germans' realistic alternatives to GDR socialism and Czech socialism, it follows that climbing over the fence into West German capitalism didn't count as a free choice. If that is in fact the type of argument you were making, then it's not substantively different from if you were to claim sex isn't a free choice unless she gets whoever she wants whether he wants her back or not.
But then, it appears that at least on some level you must already know this, because "running away from something towards an unknown is not choosing the unknown." is not the argument you were making when you wrote "How many non-capitalist choices did they have?". You're not even trying to defend that argument. "Running away from something towards an unknown is not choosing the unknown." is a new argument, a completely different argument, and, kudos to you, an incomparably better argument. If those people didn't know what they were signing up for then they weren't choosing "capitalism"; they were only choosing "something else". Fair point.
So do you figure the ten thousand-odd people who snuck out of Czechoslovakia in the first year after the communists seized power, before the new regime put up a 5000-volt electric fence to keep its subjects in, didn't know what capitalism was?