Welcome to the foster fail club
His weight sounds fine to me, I think dwarfs can vary sooo much. He's about twice the weight of Comet my robo. That weight gain was a lot in a short time, i wonder if they were feeding him up, I would have thought 49g was too light for him. Do you think he weighs more than 70g now? he looks chunky, but photos/videos can be deceiving.
I look forward to seeing the two of you getting to know each other.