If you read further down that article, you'll see it mentions Germany gave up Wituland and "parts of East Africa vital for the British to build a railway to Lake Victoria". Wituland was the northern half of what we now call Kenya, and the "parts vital" is what we now call Uganda. Germany and Britain had been disputing ownership of these territories and the Berlin Conference had ostensibly put them in the "British Sphere of Influence", but in terms of boots on the ground (northern) Kenya and Uganda were German in 1890.
And the thing is, German didn't expect to lose those territories and Britain didn't expect to get them in that treaty. The treaty was supposed to exchange German claims over Zanzibar for Heligoland - that was it, hence the name. The negotiations had proceded on those lines until, almost at the last moment, Salisbury suddenly asked for Germany to hand over Kenya and Uganda (or rather, Wituland and the interior) as well. The German ambassador had no clue why - but he eventually learnt that the Kaiser had let slip to the British ambassador in Berlin that he was desperate to have Heligoland in time for a summer ceremony that he had already planned and sent out the invitations for.
Well, fair enough - that's a strong interpretation of what happened -but German presence in Witu was almost nonexistent, and further inland, really theoretical. These were areas that Germany would have a much harder time establishing a presence in than Britain. In short, they were likely to end up in the British sphere of control anyway.
What does Wilhelm really give up at that point, anyway?
Crucially, though, before the war Britain had offered to give Kenya and Uganda back to Germany in exchange for German SW Africa (and the countries would then support each other in seizing Portugal's colonies).
When did that happen?
I've not heard that before.
The Congo doesn't give them their "German India in Africa".
Well - *nothing* in Africa would give Germany an equivalent to India - not even close.
But the Congo would give Germany a connected set of colonies reaching from Nigeria to the Indian Ocean - truly a "Mittelafrika." Even if it was mostly jungle and savannah.
In any event, in a German victory in 1914-15, the most it could reasonably hope for was to gain the Belgian Congo and keep most of its African colonies. And even that could (and would) be sacrificed if it could buy Berlin what it wanted in Europe.