Proof?
I don't even found they both apply in the same campaign or they ever participated in the same campaign. They both participating in signature campaigns, but two different campaigns, so technically they don't abuse it.
The thing they abuse is participating the merit event by fillippone, but unfortunately I don't found the rule of forbidding alt accounts.
As I mentioned earlier, even though it's extremely unlikely that he copied Stablexcoin's application, there isn't any solid evidence that proves 100% that the two accounts are related. Most likely, he was logged in from the wrong account, while it's also suspicious that Stablexcoin hasn't responded here. I'm guessing we can all understand why; because it's the same person. How is it not against the rules of signature campaigns though? I understand what you're saying, the two accounts are in different campaigns, thus, they're not abusing the said campaign, but that might as well as be a simple coincidence. One person is basically enrolled in two campaigns, receiving payment twice per week.
Anyway, as you've also seen for yourself from Awaklara's reply, the user Agbamoni is likely to have other accounts as well.