I don't really understand the answer, are they chosen by chance? So if the opponent e.g. lines up as "wishbone", will my defence maybe pick "pro" or automatically wishbone aswell?
Not by chance no, indeed if the attacker selects wishbone, the defense should play anti-wishbone. If you have multiple anti-wishbone defined in your different strategies it will take the "best" one based on the critieria (strategy building > advances > Settings for each folder).