Some examples:
The integer overflow part has incorrect binary/decimal conversions all over the place.
The example hash function used (summing elements modulo number of buckets) could be dangerous. I'm not generally a fan of showing bad practice or incorrect examples when teaching, even at an early stage when the student isn't ready for the real deal yet, but if you must then you could warn the reader that it's a simplistic example for demonstration and shouldn't be used in reality. It would not make a good impression if a candidate said they knew about hash tables but then produced that function as an example of hashing.
Similar comments apply to the treatment of big O notation. I understand that your style is to try to avoid being scary and complicated, but big O is useful because it has a specific meaning. Even in the longer explanation, you hardly mention that fundamentally it is about scalability and bounds, and you mention the danger of overlooking the constant factor only briefly right at the end. Also, the casual initial characterisation as being relative to the size of the input sets up traps when dealing with more sophisticated data structures, such as graphs where you often need to refer to the number of nodes and/or edges when specifying complexities.