This use is a very normal one. There are many Mondays in any given year - 52 of them, as you know.
When you have identified the date, but you need to clarify which day of the week, you say it that way.
My birthday is May 23, which is a Friday this year. (I think.)
My daughter's birthday is January 31. She was born on a Sunday, but even though she is now 10, next year wi