I work in addiction recovery, so I’m mainly speaking from that perspective.
From the details above, it’s not unreasonable to say that you don’t know what you don’t know. We also don’t know if this person is young and partying or old and dealing with an acute episode of grief or loneliness. If your relative’s increased drinking is not alcoholism, then we might generously say that it is about elevating feelings for pleasure or numbing out pain.
Another aspect you don’t know is that you may only be seeing some of the behavior. If it’s alcoholism, then very likely there is secrecy around drinking or drinking in isolation in addition to the public drinking. Secrecy and isolation are very common with any addiction.
One aspect of this that should be your primary focus is wrapping your head around the nature of an alcoholic’s relationship with alcohol and what that means for your boundaries in your relationship with your relative. If you are doing it right, then the bulk of your concern will be caring about your relative within the confines of those boundaries.