Nah, oceans count as "borders" here. So Brazil > Cameroon looks OK to me. And Cameroon > Nigeria is fine anyway ...
If I may, here are the original "rules" for this thread: 1. Your post must be a coin from a country which shares a border with the previously posted country. Date is not important. 2. If a country is on the ocean then any country across the ocean is acceptable as long as there is a direct, straight line between them with no intervening countries. 3. You cannot return to the previous country. That is, if the previous two countries are France and Spain you cannot return directly to France. This rules needs an exception only in the case of countries such as Lesotho, which is completely surrounded by South Africa.
The only rule that seems to be broken frequently is number 3. I interpret it to mean that you can't return to the countries in the previous two posts. That occurs quite frequently. Probably done that myself on occasion. I frequently cross the Atlantic or Pacific when a South American country is played because I don't have that many South American coins and don't want to post something I have used previously.
That rule #3 is rather ambiguous or confusing. I have always interpreted it to mean you can not return to the previous country or to the one that was just posted. Sometimes national boundaries and names change, especially in the many colonial countries of Africa.