Was it used to publish malware? Given that it's a general purpose scripting tool I can imagine that some people would abuse it and use it as some sort of backdoor to get clueless users to run malware without having to publish it on the app store.

If that's the argument I can sort of see Google's point here. The Play Store is supposed to be curated and the application should follow certain guidelines. This tool as I understand it effectively provides a loophole that lets people run non-curated code without jailbreak. I know that Apple removed apps for similar reasons in the past.

TFA is a bit misleading, the whole "AD FRAUD" angle is frankly irrelevant, it's just that since Google considers that the app violates the guidelines it can't be eligible for the ad program.