It is partly correct. The ancestors of Germanic people belonged to haplogroup I1, and a bit to I2b as well, but not I2a.
Furthermore, they did not become "Germanic" until they blended with the Indo-European R1a people (from the Corded-Ware culture) and the latter arrival of R1b from Central Europe (date unknown, but probably between 2000 and 1000 BCE). The R1b brought the centum branch of Indo-European languages that would, after fusion with the existing language, become ancient Germanic.I believe that the various IE languages that developed in Western Europe are all dialects of the Proto-Italo-Celto-Germanic, that have partially absorbed the local languages of the region where they settled. In other words, Germanic and Italo-Celtic (now Romance) languages are all IE languages hybridised with pre-existing Neolithic tongues.
The question is, did these Neolithic languages originated in the native European hunter-gatherers, in the Near-Eastern languages of the early farmers, or hybrids of both ? I prefer to favour the hybrid theory whenever in doubt. I just cannot believe that two groups of people merging into one would choose to speak only the language of one group without taking any loan words at all from the other. Naturally, one must have been dominant, at least for the grammatical structure.We will know more about this soon. The Y-DNA, mtDNA and autosomal DNA for hair and eye colour of 250 individuals from the Funnelbeaker culture (aka TRB, 4000-2700 BCE) is currently being tested in Germany. I am really looking forward to see the results. This could confirm or disprove my whole theory about the Indo-Europeans bringing haplogroups R1a and R1b to Europe, and native Europeans belonging to haplogroup I. After all, the Genographic Project of National Geographic still insist that Paleolithic Western Europeans belonged to haplogroup R1b. I have clearly explained that this didn't make sense. I hope that ancient DNA tests will prove me right.
I expect the Y-DNA results to belong primarily to haplogroup I1 or pre-I1 (a few defining mutations missing because they had not yet appeared in 3000 BCE), and possibly a bit of E1b1b, J2b and T, as Scandinavia was already a farming society.
I also think that the Indo-Europeans brought blond and red hair and blue eyes to Europe, based on the fact that all of them can be found in Central and South Asia, where haplogroup I is absent. But it is not impossible that fair hair and eyes existed in Europe before the IE migrations, if the mutations date from the Ice Age. It could very well be linked to mtDNA haplogroups U5, H1, H3 and/or V, which are found throughout Europe, including the IE homeland. But the very low incidence of fair hair and eyes among the Basques and Saami rather suggests that Europeans had dark hair and eyes before the Indo-European invasions.