I'd say that was more because that's what they thought the Well was for, he also gained knowledge of Hemalurgy and used it all while he had the power, if he managed to use Ruins magic then I seriously doubt he was significantly influenced by the Shards intent, moreover why would it be different for someone on another planet? In fact if anything Vin should be one of the people in the cosmere most effected by Preservations intent, they had a little bit of Ruin in them but were overwhelmingly of Preservation, Allomancers in particular and Vin in particular even amongst Allomancers. If the Investitude in a human had the same restrictive effects on their actions as the Intent of a Shard then Vin who has had way more contact with Preservations power than Ruin should be if anything far less likely to be able to ruin things, not only is the power of Ruin secondary to another Shard in her but that other Shard is the very opposite of Ruin.