Considering he don't join any signature campaign and high frequency of sending merit (at least 2503 times[1]), it's likely he made mistake rather than intentionally sending merit to his alt account. While it's rather rare, i have also made similar mistake (e.g. sending wrong amount of merit, sending merit to one post below/above on post i want to merit).
Seriously?! 
We are not talking about trained monkey who is using keyboard to make multiple ''mistakes'' like this to his alt accounts, and add them to his trust list.
If you ever try to send lots of merit at once, you might understand what i meant. It's different case for adding his alt. account into trust list.