It's difficult to steal something offered for free. You could try to charge them with attempted DDOS or something like that but since wikimedia did not suffer any actual degradation of service. I think that at most you can go for something like "causing harmful traffic through negligence" but you'd need to prove the traffic was actually harmful.
In any case let's not get carried away. 90 million requests for a 70KB file is only 5.8 TB. Wikimedia mentions in their about pages that they are hosted on bare metal servers in various places around the world. Just going on the bandwidth charges of the first provider in the list, that'd be about $30 USD per month if they have the "bulk" pricing or $300 USD per month if they use the list pricing. I don't think that is worth going to court over for the Wikimedia foundation.
In any case let's not get carried away. 90 million requests for a 70KB file is only 5.8 TB. Wikimedia mentions in their about pages that they are hosted on bare metal servers in various places around the world. Just going on the bandwidth charges of the first provider in the list, that'd be about $30 USD per month if they have the "bulk" pricing or $300 USD per month if they use the list pricing. I don't think that is worth going to court over for the Wikimedia foundation.