Translation:The house was drawn by a Finnish architect.
Yes, the difference in meaning is very small. är ritat av emphasizes the result, and ritades emphasizes the process, so if you're telling a story about how it happened, the latter will be better, but if you just want to state who 'drew' the house, the first is better. But it's a small difference.
It isn't supposed to be in the past tense in Swedish – the Swedish sentence only means that the action of drawing took place in the past + the result of that action remains in the present.
In English, it seems that was drawn is the best translation of this. If you say the house is drawn, that could mean that the house 'is being drawn right now' which is not what the Swedish sentence means.
How English and Swedish correspond here is a bit tricky though.
The sentence only really sounds ‘off’ because of the lack of context. If it’s obvious that it’s a blueprint or architectural drawing of a house being discussed, then it sounds just fine, but the verb ‘draw’ doesn’t imply that without further context in English (and outside of engineering/architectural contexts, it’s very rare to use it that way, at least here in the US Midwest), which is why there’s the preference among comments for ‘designed’ instead.
Personally, I would probably use ‘drafted’ instead however because, while somewhat less common, it’s completely unambiguous (in this context, it can only logically refer to the process of producing blueprints or architectural drawings).
It looks very much that Duolingo struggles here in this section with how the translation should be. In this sentence the translation is "was......" and "is....." is marked wrong, in other sentences both are accepted, and sometimes only "is...." is accepted". This inconsistancy makes it very confusing.