Also, the key word here is "reported," because anyone who pays any attention knows companies don't always report or fix flaws/bugs that are found.
The most interesting thing I see here is that Intel is a mix of internal and (a significant amount of) bounty finds, whereas AMD is entirely external, which I assume means flaws found and reported for no compensation. This suggests a few things: AMD doesn't seem to do nearly as much as Intel at finding issues with their own chips, they don't appear to have a bug bounty which, along with the first point, indicates they're not as concerned as Intel at finding issues, and without a reward for reporting flaws, there won't be as much effort put into finding them, which could be part of the reason for the lower numbers, and the likelihood of someone that finds one actually reporting it is lower, so there may be more unknown (to the companies and public) ones than with Intel.