What leads me is the fact that he's able to escape from his rivals when the road goes uphill, which wasn't the case in the Giro. What leads me is also the fact that he lost 1.45 min less in the TT similar length to stage winner. To me these are convincing indicators of his form.
I think Lopez was strong in the Giro, too. As evident from his surprisingly good performance in the opening ITT where he beat Dumoulin among others. But he had his misfortunes and was very incosistent.
I think the main protagonists from the Giro and Vuelta are comparable in strength. If you want to evaluate MAL's strength in both GTs, look at Majka. He is the same 2nd tier GT contender who competes for positions from 5th to 10th. He was in 6th in the end at the Giro, one position ahead of Lopez. Right now in the Vuelta there's no comparison. Lopez is one or two levels above Majka right now and is 4min ahead of him in GC. So if he stays consistent I think it's safe to say his level is better than it was during the Giro.