I can't think of any scenario in which deliberately tanking the world's economy makes economic sense.
Are you familiar with Nero? He wanted to buy some property, the people didn't want to sell it so he started a fire and then kept the fire department from putting it out. After the fire he was able to buy the land at a discount.
Also who creates a bio weapon that only kills 1% of its victims?. .
I don't think China released it on purpose or what they did do was lie until it was too late to do anything about it.