Mixed breeds don't always have the same exact look because they may show more of one of the parents than the other. The tail and hair look right for those breeds. There is a different look with the one on the left, especially the ears. May have a third breed there and the face does not have the feathering. Even so looks like a wonderful little puppy. Might be beagle. You can always do a DNA test for the dog if you really want to know. Hope that helps.
Because a Maltese Shih Tzu is a mix between two breeds, you're going to see a wide range of physical and behavioral traits in the puppies. They're going to be a lot more unpredictable than a purebred for this reason, especially if the puppies in question were multi-generation mixes (meaning that one or both parents were also Maltese x Shih Tzu crosses).
So it's entirely possible both puppies are the same cross. It's also possible that one or both puppies have a different parentage than what you were told. Some of the reputable DNA tests might give you a clearer answer, but even they aren't 100% accurate and can only tell you about three generations back, so if another breed was mixed in a few generations ago it'll be hard to tell for sure.
The one on left looks more like my augie puppies.
It has no bearding which both Maltese (appearance basically a pure whit shitzu) and ShiTzu have. Did they actually come from same place? Not that guarantees there a not an extra unauthorized breeding.