Learn Turkish: Kâşif ormanda bir pusu beklemiyordu. - The explorer was not expecting an ambush in the jungle.

beklemiyordu is the past continuous and simply states a fact about what was happening: "was not expecting." If we used the lesson's target grammar, bekleyemezdi, it would mean "could not have expected" or "would not have been able to expect." This sentence focuses on the reality of his thoughts at that moment, not a theoretical lack of ability.

Why doesn't bir pusu take the accusative case suffix (like bir pusuyu)?

Because it is an indefinite direct object. The explorer wasn't expecting a specific known ambush ("the ambush"), just "an" ambush in general. In Turkish, indefinite direct objects do not take the accusative case marker and must sit directly in front of the verb.

The verb root is bekle-, so shouldn't the negative past continuous be beklemeyordu?

This is a classic example of vowel narrowing, which is always good to remember. When the continuous suffix -yor attaches to a syllable ending in a wide vowel like 'a' or 'e' (in this case, the negative suffix -me), it narrows that vowel to 'ı', 'i', 'u', or 'ü'. Therefore, bekle-me-yor-du shifts to beklemiyordu.

What is the purpose of the circumflex (^) on Kâşif?

In loanwords from Arabic and Persian, the circumflex softens or palatalizes the preceding consonant (making the 'k' sound a bit like 'ky') and slightly lengthens the vowel. While some circumflexes are dropped in modern informal Turkish, keeping it on words like kâşif (explorer) is standard and guides the correct pronunciation.