Not at all. Whomever says grades define intelligence is very small-minded. Intelligence comes in so many forms. Even people with so called “learning disabilities” that are seen as “dumb,” usually are very intelligent in other ways.
For example, one person may be book smart, and another may be street smart. Another person might be both of those things. A person could be very skilled with mathematics and science, and struggle with English literature. Nonetheless, Intelligence really isn’t something that can be measured; it is not concrete enough.
Something important to keep in mind: “Everyone is a genius. However, if you judge a fish by its inability to climb a tree, it will live its whole life believing it is stupid.”