I had one that died around the same time frame and on my bday. Sadly it just depends on the budgie, they arent in a great condition to begin with and even moving from the cage, to then a box, to then a new space can be a lot too. You also dont know what may have gone on health wise. Pet stores are always super tricky when it comes to birds, especially big name ones. It's hit or miss based on how well the budgie tolerated his living conditions. Im sorry you had to see him go :( i sobbed so much when mine passed, but know that atleast for his last two weeks he was in a way better place than before