First of all, that link is from 2006, before much research had been done into I1 STR diversity. Secondly, read it more closely:
Basically he's saying that based on what he knew at the time (back in 2006) it seemed more likely that the migration pattern was Slovenia to Scandinavia rather than Scandinavia to Slovenia, but he refused to rule out a Germanic migration into the Balkans.
But a Germanic migration into the Balkans is what seems more likely now. Take a look at Slovenian samples in the
I1 Project. None stretch their STR patterns outside of existing, principally Germanic clusters like AS-gen and T2. The best explanation for them now is likely East Germanic origin.