Learning music does imply a certain facility with figures, purely in order to count lengths of notes, and do simple ratios (two of these notes in the space of one of those), multiplication (if this note has a dot, how long does it last? or with two dots?) and addition (these two notes are tied, how long does the combined note last?) to get all the notes in the right relative places to play the piece. Music also helps with identifying sequences, by means of chords and scales and intervals. Not high-level maths, certainly, but certainly for children it means that they're practising one while practising the other, so an ability at one will help the other purely in terms of time spent practising. A child who doesn't play will just do their maths homework then stop, not really apply the skill again till the next maths lesson, while a child learning an instrument does their maths homework then goes and spends some time reinforcing its basic principles by playing.
One of the classic combinations of subjects that 'go' together is maths, physics, music and languages. Maths and music as they are related skills, and physics in the same sense as it is application of maths and also relates easily into music, and languages as ability at maths and music imply an ability to practise and remember structures to form a piece of music or a sentence.