You will notice in the Radix explorer validator list (and other community sites) that as well as the validator fee and uptime, the “Owner Stake” is also provided.
The owner stake is the amount of XRD that the validator owner has delegated to their own node and is a measure of how much “skin in the game” they have.
In the future when slashing is implemented (see here: Slashing) the owner stake will help to signify how much personal stake the validator is risking and can be used as a way of determining whether or not they are likely to engage in any malicious behaviour.
However, some validators elect not to use the owner wallet for their personal staking and choose to stake from an alternative wallet. This could be for a number of honest reasons, such as wanting to separate their income between fees and staking and is not necessarily a cause for concern. In this case, it is advisable to contact the validator to understand their reasoning.