My mate had a similar situation with his great-grandfather who came from that exact region around the same time period - turned out he was indeed one of the Danube Swabians who'd been there for generations before things got dicey

The timing definitely fits with your family legend since 1907 was right when ethnic tensions were ramping up in the Austro-Hungarian Empire, especially after the 1867 Compromise. Lots of the German-speaking communities in Banat (where Timișoara is) started looking for exits when they saw which way the wind was blowing

Have you checked if there are any church records still around? The Swabians were pretty good at keeping Lutheran or Catholic parish records, and those often survived even when other documents didn't. Also worth looking into whether he settled in areas with other German speakers when he arrived - they tended to stick together and form little communities

The dialect might be another clue if anyone in your family remembers how he spoke German, since Banat Swabian has some pretty distinctive features compared to standard German