When two languages collide

Botchan Karakuri Clock, Dogo Onsen Station, Matsuyama, Ehime
(I have a fragile head during cold wind season -____-)

Last week, my lecturers from my former university came to Matsuyama. They came to participate in an international conference. They were Bu Zullies and Bu Triana. Bu Zullies came with her children as well.

Bu Zullies was a student of Ehime University while Bu Triana graduated from Düsseldorf University Germany. Both countries have their own mother language, Japanese and German. Since they lived abroad for doctoral study, the languages will somehow stuck in their mind, right?

During the conversation, I kept hearing them saying "ahsooo" in an intonation to show that they finally understood about something. In Indonesia, it is heard like "oh gituuuuu"

The funny thing is, since I currently live in Japan and I ever lived in German, I exactly knew what they were saying:

Bu Zullies was saying, "ああそう!" It is pronounced "aasoou", but somehow it is heard as "ahsoo". While Bu Triana was saying, "ach so!" and it is pronounced "ahsoo".

Is it homophone or it is not?

Indeed, these two words mean "oh gituuuuu.."