Why should the adverb imply a particular tense? It's like expecting "just" in English to be used only with present... thinkng about it, 'soeben' seems to be used much like 'just' is. I just came back is borderline past/present. You would not place it on the same timeline spot as 'i only came back', 'i then came back', and it would be much closer to 'i have just come back' or 'i'm just coming back' -with the right context for that last one, granted.
So well, no WTF material here imho, just room for being subtle in German, as you can be in English
there's synonymous, although it seems German folks prefer to use "gerade" more colloquially :
you may be right, but DL is not consistent with these things. For instance in a similar sentence "Ich komme soeben aus dem Krankenhaus" , DL accepts the translation "I just come from the hospital" as well as "I just came from the hospital". In an instructive program such inconsistencies can not be approved.