I have no idea where that figure came from, I haven't seen it, but some confuse a theoretical risk with an actual risk. From the beginning of HIV it was assumed it could be spread through oral sex since the virus was present, but nobody who was contact traced ever got it who only engaged in oral sex. This has been true ever since, so while a scientist will never say you can't get it that way, that's not how science is done, they will tell you they've never found anyone who got it that way. That being the case, that 7% figure is obviously wrong or misinterpreted.
Regarding the "7 percent of cases are from this situation". It looks like someone was lying. This is the problem with research, people who are participating in the survey for research purposes can lie or leave out information. And so certain journals will take this and publish it. I would put to rest your worry about getting HIV from performing falacio on a male, as the risk for that is non-existent.
I've also seen that figure mentioned, but what I have NOT seen is any evidence to support it.
From the HIV expert doctor (Edward Hook) who used to post on this site:
"As far as HIV is concerned, there is no known risk of getting HIV from performing oral sex on an infected partner, even if that person's genital secretions get into your eyes or if you swallow."
"HIV is not spread by oral sex, giving or receiving, even if sores, gum disease or blood is present."
"The fact is that there are no cases in which HIV has been proven to be transmitted by oral sex, including fellatio."
Here is a study involving serodiscordant couples that supports these statements: https://www.ncbi.nlm.nih.gov/pubmed/12045500