The description of the map states that it's " A simplified map of alliances between May and August of 1975.", which is a bit weird, but since it's Wikipedia we can forgive it. (Can we? I'm not sure, but we'll forgive them anyway)

Anyhow, the Portuguese were one of the last colonial powers to hand back their colonial possessions to the indigenous population, which only happened after long wars of independence in the colonies, which I'm not really qualified to explain in-depth.

Needless to say, wars aren't really popular the longer they drag on, so eventually this led to a military coup back in Portugal to overthrow the Authoritarian Estado Novo regime which was trying to hold on to the colonies. This coup happened in 1974, one year before the date wikipedia puts on the map, and they decided to start the process of decolonisation. Ceasefires were declared in 1974, but the official date of independence was the 25th of June 1975 for Mozambique, and 11 November 1975 for Angola.

So as a final answer to your question, the period the map chose was the period just before the formal independence of those countries, making them still officially a part of Portugal even though de facto the situation was already different. I'm sorry for being sparse with details, but as I said I don't think I'm in any way qualified to explain further because I know very little about that period.

As an extra bonus, here's a cool map (~guessing it was made around 1918-1939 based on pre-WW2 borders) of the Portuguese colonial possessions, titled "Portugal is not a small country", overlaid over Europe. http://i.imgur.com/I9T6A0Q.jpg