Breakdown of Sami wybraliśmy autostradę, tymczasem oni pojechali przez las.
oni
they (masculine personal)
las
forest
sam
alone / himself (emphatic) / pure / nothing but
przez
through, across
Questions & Answers about Sami wybraliśmy autostradę, tymczasem oni pojechali przez las.
Does tymczasem mean 'meanwhile' as a time reference, or 'whereas' as a contrast here?
It actually does both! While tymczasem literally means 'in the meantime', it is frequently used in Polish as a discourse marker to show strong contrast between two parallel situations. Here, it translates best to 'whereas', highlighting the differing choices between the two groups.
Could we use the connector za to instead of tymczasem in this sentence?
It wouldn't sound natural here. The connector za to is used for trade-offs or compensation, translating closer to 'but in return' or 'on the upside'. Since going through the forest isn't a direct compensation for someone else taking the highway, tymczasem is the correct choice for pure contrast.
Why does the sentence start with sami rather than the pronoun my?
By dropping my (which is already implied by the verb ending in -liśmy) and using sami, the sentence heavily emphasizes that 'we did it ourselves' or 'we made the choice on our own'. If the speaking group consisted entirely of women, this would change to the non-masculine personal form same.
Why is the perfective verb pojechali used here instead of the imperfective jechali?
Pojechali treats their action of taking the forest route as a completed, single event. If you used the imperfective jechali, it would focus on the duration, meaning 'whereas they were driving through the forest', which doesn't contrast as cleanly with the single completed choice of taking the highway.