There's nothing wrong with the sentences. It is rather an extension of usage.
[sic] can mean that something is not correct in a quote (typo etc) but you could also use it to emphasize some peculiarity of the quoted text (e.g. contradictory or
dubious assertions or a value that deviates heavily from the norm). By using [sic] you normally want to express that ...
The English straight double quotation mark "" was an invention of the typewriter era.
Because typewriters worked by mechanical devices at that time, the number of keys had to be minimized, so this type of quotation mark was invented as a last resort.
Technically, we don't use typewriters anymore, so there is no key-number restriction and avoid ...
The awkwardly worded example could be re-written as follows, where it's still evident that these are all Dave Thomas's ideas.
According to Dave Thomas, the Whopper is a great sandwich. It has
lettuce, tomato, and even mayonnaise. It's flame broiled, which means
it's cooked over an open flame. The bun is topped with sesame seeds,
which add a nice crunch. He ...