Welcome to the community @Abhay
I believe this is just the way Klaviyo stores dates as MM DD YYYY. Your birthday date property format is set to MM DD so Klaviyo has added 2016 as the year (not sure why that date!).
However, this will not impact your birthday flow as Klaviyo triggers this based on the MM DD and it is usual to set this flow to repeat annually.
Regarding your second question, it’s not possible to preview the trigger for a date-based flow. However, you can test by setting your flow trigger to ‘On date property’ and set your flow emails to manual. Then on a test profile, set the birthday to tomorrow’s date MM/DD/YYYY. Then look at the first email in your flow and click ‘View Details’ and then ‘Recipient Activity. In the waiting tab you should see your test profile and that it is is scheduled for tomorrow at the time you’ve specified in the trigger.
When you’re happy, set the flow emails to live, or keep at manual for a while to review actual profiles as the enter the flow.
Hope that helps
Andy