The acoustic difference between voiced, tenuis (voiceless unaspirated), and aspirated stops mostly comes down to voice onset time: the difference in time between the release of the stop and the start of voicing. If voicing starts before the stop is released, it's more "voiced". If it starts significantly later, it's more "aspirated".
Note though that this is a continuous value rather than a discrete one. In other words, you can have an extremely voiced stop, or a slightly voiced stop, or anywhere in between. Different languages draw boundaries in different places on this continuum to break it up into discrete categories. For example, English and Spanish both have a two-way distinction: stops that fall on one side of the dividing line are "voiced", and stops on the other side are "voiceless". But the boundary line for English is more on the "aspirated" side, and the boundary line for Spanish more on the "voiced" side, meaning that quite a lot of English "voiced" stops can sound "voiceless" to Spanish-speakers and vice versa. (For this reason, some phonologists prefer to use the terms "lenis" and "fortis", to make it clear that they're talking about a language-specific phonological boundary rather than something universal.)
Presumably the same thing is happening here. Stops that fall into the category of "voiced" for you, fall into the category of "tenuis" for your listener, since the boundaries are drawn in different places in their native language. Their "voiced" stops are probably even more voiced, with even more voicing happening before the release of the stop.