There were a lot of Googlable boilerplate questions (e.g. "what does malloc return?", "what's a bloom filter?") that, as a product engineer, never come up.
Then there were the classic Big-O notation queries that for most use cases don't come up until much later stage. It felt like the founders were classically trained in CS and over-optimizing for things that aren't practically relevant for the large majority of early/mid-stage startups.
Am I familiar with these concepts—e.g. can I go back and refresh myself when they come up?—absolutely. But often times the skills you'd want in an engineer are:
1. Knowing when to optimize
2. Knowing how to profile and identify bottlenecks
3. Familiarity with the available solutions
4. Ability to dig in and evaluate which is the right tool for the jon